UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM10-K

(Mark One)

For the fiscal year ended December 31, 20182019

or

For the transition period fromto

333-189017-07

(Commission File Number of issuing entity)

0001629716

(Central Index Key Number of issuing entity)

Citigroup Commercial Mortgage Trust 2015-GC27

(Exact name of issuing entity as specified in its charter)

333-189017

(Commission File Number of depositor)

0001258361

(Central Index Key Number of depositor)

Citigroup Commercial Mortgage Securities Inc.

(Exact name of depositor as specified in its charter)

Citigroup Global Markets Realty Corp.

(Central Index Key Number: 0001541001)

Goldman Sachs Mortgage Company

(Central Index Key Number: 0001541502)

Rialto Mortgage Finance, LLC

(Central Index Key Number: 0001592182)

Redwood Commercial Mortgage Corporation

(Central Index Key Number: 0001567746)

RAIT Funding, LLC

(Central Index Key Number: 0001587045)

(Exact name of sponsor as specified in its charter)

c/o Citibank, N.A.

388 Greenwich Street, 14^th Floor

New York, New York 10013

(Address of principal executive offices of issuing entity)

(212)816-5614

Registrant’s telephone number, including area code

Securities registered pursuant to Section 12(b) of the Act:

Securities registered pursuant to sectionSection 12(g) of the Act:  None.

None

Indicate by check mark if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act.    ☐  Yes    ☒  No

Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or Section 15(d) of the

Act.    ☐  Yes    ☒  No

Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days.    ☒  Yes    ☐  No

Indicate by check mark whether the registrant has submitted electronically every Interactive Data File required to be submitted pursuant to Rule 405 of RegulationS-T (§ 232.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit such files).

Not Applicable

Indicate by check mark if disclosure of delinquent filers pursuant to Item 405 of RegulationS-K (§ 229.405 of this chapter) is not contained herein, and will not be contained, to the best of registrant’s knowledge, in definitive proxy or information statements incorporated by reference in Part III of this Form10-K or any amendment to this Form10-K.

Not Applicable

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company, or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company,” and “emerging growth company” in Rule 12b-2 of the Exchange Act.

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act.    ☐

Indicate by check mark whether the registrant is a shell company (as defined in Rule12b-2 of the Act).    ☐  Yes    ☒  No

State the aggregate market value of the voting andnon-voting common equity held bynon-affiliates computed by reference to the price at which the common equity was last sold, or the average bid and asked price of such common equity, as of the last business day of the registrant’s most recently completed second fiscal quarter.

Not Applicable

Indicate by check mark whether the registrant has filed all documents and reports required to be filed by Section 12, 13 or 15(d) of the Securities Exchange Act of 1934 subsequent to the distribution of securities under a plan confirmed by a court.

Not Applicable

Indicate the number of shares outstanding of each of the registrant’s classes of common stock, as of the latest practicable date.

Not Applicable

DOCUMENTS INCORPORATED BY REFERENCE

List hereunder the following documents if incorporated by reference and the Part of the Form10-K (e.g., Part I, Part II, etc.) into which the document is incorporated: (1) Any annual report to security holders; (2) Any proxy or information statement; and (3) Any prospectus filed pursuant to Rule 424(b) or (c) under the Securities Act of 1933. The listed documents should be clearly described for identification purposes (e.g., annual report to security holders for fiscal year ended December 24, 1980).

Not Applicable

PART I

Item 1. Business.

Omitted.

Item 1A. Risk Factors.

Omitted.

Item 1B. Unresolved Staff Comments.

None.

Item 2. Properties.

Omitted.

Item 3. Legal Proceedings.

Omitted.

Item 4. Mine Safety Disclosures.

Not applicable.

PART II

Item 5. Market for Registrant’s Common Equity, Related Stockholder Matters and Issuer Purchases of Equity Securities.

Omitted.

Item 6. Selected Financial Data.

Omitted.

Item 7. Management’s Discussion and Analysis of Financial Condition and Results of Operations.

Omitted.

Item 7A. Quantitative and Qualitative Disclosures About Market Risk.

Omitted.

Item 8. Financial Statements and Supplementary Data.

Omitted.

Item 9. Changes in and Disagreements With Accountants on Accounting and Financial Disclosure.

Omitted.

Item 9A. Controls and Procedures.

Omitted.

Item 9B. Other Information.

None.

PART III

Item 10. Directors, Executive Officers and Corporate Governance.

Omitted.

Item 11. Executive Compensation.

Omitted.

Item 12. Security Ownership of Certain Beneficial Owners and Management and Related Stockholder Matters.

Omitted.

Item 13. Certain Relationships and Related Transactions, and Director Independence.

Omitted.

Item 14. Principal Accounting Fees and Services.

Omitted.

ADDITIONAL DISCLOSURE ITEMS REQUIRED BY GENERAL INSTRUCTION J(2)

Item 1112(b) of Regulation AB

With respect to the pool assets for Citigroup Commercial Mortgage Trust 2015-GC27, there are no significant obligors within the meaning of Item 1101(k) of Regulation AB.

Item 1114(b)(2) and Item 1115(b) of Regulation AB

No entity or group of affiliated entities provides any external credit enhancement, uses any derivative instruments or other support for the certificates within this transaction.

Item 1117 of Regulation AB

Disclosure from Citibank, N.A., as Certificate Administrator:

Citibank, N.A. (“Citibank”) is acting as the Certificate Administrator of this commercial mortgage-backed securities (“CMBS”) transaction. In the ordinary course of business, Citibank is involved in a number of legal proceedings, including in connection with its role as trustee of certain residential mortgage-backed securities (“RMBS”) transactions. Certain of these Citibank as trustee-relatedtrustee related matters are disclosed herein.

On June 18, 2014, a civil action was filed against Citibank in the Supreme Court of the State of New York by a group of investors in 48 private-label RMBS trusts for which Citibank allegedly serves or did serve as trustee, asserting claims for purported violations of the U.S. Trust Indenture Act of 1939, as amended (the “Trust Indenture Act”“TIA”), breach of contract, breach of fiduciary duty and negligence based on

Citibank’s alleged failure to perform its duties as trustee for the 48 RMBS trusts.  On November 24, 2014, plaintiffs sought leave to withdraw this action.  On the same day, a smaller subset of similar plaintiff investors in 27 private-label RMBS trusts for which Citibank allegedly serves or did serve as trustee, filed a new civil action against Citibank in the United States District Court for the Southern District of New York asserting similar claims as the prior action filed in state court.  In January 2015, the court closed plaintiffs’ original state court action.  On September 8, 2015, the federal court dismissed all claims as to 24 of the 27 trusts and allowed certain of the claims to proceed as to the other three trusts.  Subsequently, plaintiffs voluntarily dismissed all claims with respect to two of the three trusts.  On April 7, 2017, Citibank filed a motion for summary judgment.  Plaintiffs filed its consolidated opposition brief and cross motion for partial summary judgment on May 22, 2017.  Briefing on those motions was completed on August 4, 2017.  On March 22, 2018, the court granted Citibank’s motion for summary judgment in its entirety, denied Plaintiffs’plaintiffs’ motion for summary judgment and ordered the clerk to close the case.  On April 20, 2018, plaintiffs filed a notice of appeal.  Plaintiffs’ opening brief was filed on August 3, 2018.  Citibank filed its opposition on November 2, 2018.  Plaintiffs’Plaintiffs filed their reply on November 16, 2018.  On June 7, 2019, the Second Circuit dismissed the plaintiffs’ appeal following the parties’ filing of a stipulation withdrawing the case with prejudice pursuant to Federal Rule of Appellate Procedure 42.

On November 24, 2015, the same investors that brought the federal case brought a new civil action in the Supreme Court of the State of New York related to 25 private-label RMBS trusts for which Citibank allegedly serves or did serve as trustee.  This case includes the 24 trusts previously dismissed in the federal action, and one additional trust.  The investors assert claims for breach of contract, breach of fiduciary duty, breach of duty to avoid conflicts of interest, and violation of New York’s Streit Act (the “Streit Act”“Streit Act”).  Following oral argument on Citibank’s motion to dismiss, plaintiffs filed an amended complaint on August 5, 2016.  On June 27, 2017, the state court issued a decision, dismissing the event of default claims, mortgage-file-related claims, the fiduciary duty claims, and the conflict of interest claims.  The decision sustained certain breach of contract claims including the claim alleging discovery of breaches of representations and warranties, a claim related to robo-signing, and the implied covenant of good faith claim.  Citibank appealed the lower court’s decision, and on January 16, 2018, the Appellate Division, First Department, dismissed the claims related to robo-signing and the implied covenant of good faith, but allowed plaintiffs’ claim alleging discovery of breaches of representations and warranties to proceed.  On June 7, 2019, plaintiffs filed a motion for discontinuance of the action and dismissal of plaintiffs’ claims with prejudice.

On August 19, 2015, the Federal Deposit Insurance Corporation (“FDIC”)FDIC as receiver for a failed financial institution filed a civil action against Citibank in the Southern District of New York.  This action relates to one private-label RMBS trust for which Citibank formerly served as trustee.  The FDIC asserts claims for breach of contract, violation of the Streit Act, and violation of the Trust Indenture Act.TIA.  Citibank jointly briefed a motion to dismiss with The Bank of New York Mellon and U.S. Bank, N.A., entities that have also been sued by the FDIC in their capacity as trustee, and these cases have all been consolidated in front of Judge Carter.  On September 30, 2016, the court granted theCitibank’s motion to dismiss without prejudice for lack of subject matter jurisdiction.  On October 14, 2016, FDIC filed a motion for reargument or relief from judgment from the court’s dismissal order.  On July 11, 2017, Judge Carter ruled on the motion for reconsideration regarding his dismissal of the action.  He denied reconsideration of his decision on standing, but granted leave to amend the complaint by October 9, 2017.  The FDIC subsequently requested an extension of time to file its amended complaint, which was granted.  The FDIC filed its amended complaint on December 8, 2017.  Defendants jointly filed a motion to dismiss the amended complaint on March 13,and that joint motion was fully briefed as of May 3, 2018.  On March 20, 2019, the court granted defendants’ joint motion to dismiss the amended complaint.  The FDIC’s deadline to file a notice of appeal was April 18, 2018, plaintiff filed its opposition. Defendants filed their joint reply on May 3, 2018.22, 2019.  The FDIC has not appealed.

There can be no assurances as to the outcome of litigation or the possible impact of litigation on the trustee or the RMBS trusts.  However, Citibank denies liability and continues to vigorously defend against these litigations.  Furthermore, neither the above-disclosed litigations nor any other pending legal proceeding involving Citibank will materially affect Citibank’s ability to perform its duties as Certificate Administrator under the poolingPooling and servicing agreementServicing Agreement for this CMBS transaction.

Disclosure from Deutsche Bank Trust Company Americas, as Trustee:

Deutsche Bank Trust Company Americas (“DBTCA”) and Deutsche Bank National Trust Company (“DBNTC”) have been sued by investors in civil litigation concerning their role as trustees of certain residential mortgage-backed securities (“RMBS”)RMBS trusts.

On June 18, 2014, a group of investors, including funds managed by Blackrock Advisors, LLC, PIMCO-Advisors, L.P., and others, filed an action against DBNTC and DBTCA in New York State Supreme Court alleging that DBNTC and DBTCA failed to perform purported duties, as trustees for 544 private-label RMBS trusts, to enforce breaches of representations and warranties as to mortgage loans held by the trusts and to enforce breaches by servicers of their mortgage loan servicing obligations for the trusts.  During the course of the litigation, plaintiffs dismissed the case from New York State Supreme Court and refiled two separate cases, one in the U.S. District Court for the Southern District of New York (the “BlackRockSDNY Case”) and the other in the Superior Court of California, Orange County (the “BlackRockCalifornia Case”).  Pursuant to a settlement among the parties, theBlackRockSDNY Case was dismissed on December 6, 2018 and theBlackRockCalifornia Case was dismissed on January 11, 2019.

On September 27, 2017, DBTCA was added as a defendant to a case brought by certain special purpose entities including Phoenix Light SF Limited in the U.S. District Court for the Southern District of New York, in which the plaintiffs previously alleged incorrectly that

DBNTC served as trustee for all 43 of the trusts at issue.  On September 27, 2017, plaintiffs filed a third amended complaint that names DBTCA as a defendant in addition to DBNTC.  DBTCA serves as trustee for one of the 43 trusts at issue.  DBNTC serves as trustee for the other 42 trusts at issue.  Plaintiffs’ third amended complaint brings claims for violation of the U.S. Trust Indenture Act of 1939 (“TIA”); breach of contract; breach of fiduciary duty; negligence and gross negligence; violation of New York’s Streit Act (the “Streit Act”);Act; and breach of the covenant of good faith.  However, in the third amended complaint, plaintiffs acknowledge that, before DBTCA was added to the case, the court dismissed plaintiffs’ TIA Act claims, negligence and gross negligence claims, Streit Act claims, claims for breach of the covenant of good faith, and certain theories of plaintiffs’ breach of contract claims, and plaintiffs only include these claims to preserve any rights on appeal.  Plaintiffs allege damages of “hundreds of millions of dollars.”  On November 13, 2017, DBNTC and DBTCA filed an answer to the third amended complaint.  On December 7, 2018, DBNTC and DBTCA filed a motion for summary judgment.  Also on December 7, 2018, plaintiffs, jointly with Commerzbank AG (see description ofCommerzbank case below), filed a motion for partial summary judgment.  As of March 1, 2020, both motions for summary judgment have been briefed and are awaiting decision by the court.

On November 30, 2017, DBTCA was added as a defendant to a case brought by Commerzbank AG (“Commerzbank”) in the U.S. District Court for the Southern District of New York, in which Commerzbank previously alleged incorrectly that DBNTC served as trustee for all 50 of the trusts at issue.  On November 30, 2017, Commerzbank filed a second amended complaint that names DBTCA as a defendant in addition to DBNTC.  DBTCA serves as trustee for one1 of the 50 trusts at issue.  DBNTC serves as trustee for the other 49 trusts at issue.  Commerzbank’s second amended complaint brings claims for violation of the TIA; breach of contract; breach of fiduciary duty; negligence; violation of the Streit Act; and breach of the covenant of good faith.  However, in the second amended complaint, Commerzbank acknowledges that, before DBTCA was added to the case, the court dismissed Commerzbank’s TIA claims for the trusts governed by pooling and servicing agreements, as well as its Streit Act claims and claims for breach of the covenant of good faith, and Commerzbank only includes these claims to preserve any rights on appeal.  The second amended complaint alleges that DBNTC and DBTCA caused Commerzbank to suffer “hundreds of millions of dollars in losses,” but the complaint does not include a demand for money damages in a sum certain. On January 29, 2018, DBNTC and DBTCA filed an answer to the second amended complaint.  On December 7, 2018, DBNTC and DBTCA filed a motion for summary judgment.  Also on December 7, 2018, Commerzbank, jointly with thePhoenix Lightplaintiffs, filed a motion for partial summary judgment.  As of March 1, 2020, both motions for summary judgment have been briefed and are awaiting decision by the court.

On December 30, 2015, IKB International, S.A. in Liquidation and IKB Deutsche Industriebank A.G. (collectively, “IKB”), as an investor in 37 RMBS trusts, filed a summons with notice in the Supreme Court of the State of New York, New York County, against DBNTC and DBTCA as trustees of the trusts.  On May 27, 2016, IKB served its complaint asserting claims for breach of contract, breach of fiduciary duty, breach of duty to avoid conflicts of interest, violation of the Streit Act, violation of the TIA, violation of Regulation AB, and violation of Section 9 of the Uniform Commercial Code.  IKB alleges that DBNTC and DBTCA are liable for over U.S. $268 million in damages.  On October 5, 2016, DBNTC and DBTCA, together with several other trustees defending lawsuits by IKB, filed a joint motion to dismiss.  On January 6, 2017 and June 20, 2017, IKB voluntarily dismissed with prejudice all claims as to seven trusts.  As of March 1, 2019,2020, DBNTC and DBTCA’s motion to dismiss has been briefed and is awaiting decision by the court.

It is DBTCA’s belief that it has no pending legal proceedings (including, based on DBTCA’s present evaluation, the litigation disclosed in the foregoing paragraphs) that would materially affect its ability to perform its duties under the related servicing agreement for this transaction.

Item 1119 of Regulation AB

Provided previously in (i) the prospectus supplement of the Registrant relating to the issuing entity and filed on February 9, 2015 pursuant to Rule 424(b)(5) of the Securities Act of 1933, as amended and (ii) the Current Report on Form 8-K filed by the registrant on July 5, 2018 under Commission File No. 333-189017-07.

Item 1122 of Regulation AB

The reports on assessment of compliance with servicing criteria for asset-backed securities and related attestation reports are attached hereto under Item 15.

The report on assessment of compliance with applicable servicing criteria furnished pursuant to Item 1122 of Regulation AB by Midland Loan Services, a Division of PNC Bank National Association (“Midland”) discloses that a material instance of noncompliance occurred, as described below:

Material Instance of Noncompliance

In certain instances, the Schedule AL Files (Item 1125 of Regulation AB) were not reported in accordance with the terms specified in the transaction agreements, in conflict with Item 1122(d)(3)(i): “Reports to investors, including those to be filed with the Commission, are maintained in accordance with the transaction agreements and applicable Commission requirements. Specifically, such reports: (A) Are prepared in accordance with timeframes and other terms set forth in the transaction agreements”. The noncompliance consisted of omitted or inaccurately reported numbers due to the following: (1) the initial setup files contained information at the asset level, and Midland was required to manually compile the information to present it at the loan level as required by Schedule AL; and (2) certain reporting requirements required manual processing by Midland, including the use of various data computation formulas, quality control checks and analysis.

The identified instances did not involve the servicing of the assets backing the asset-backed securities covered in this Form 10-K report.

Steps Taken to Remedy the Material Instance of Noncompliance

Midland is currently remediating the Schedule AL reporting for the CMBS transactions found to be incorrect, and will be making improvements to its systems, processes and procedures to support its Schedule AL reporting obligations.

Item 1123 of Regulation AB

The servicer compliance statements are attached hereto under Item 15.

PART IV

Item 15. Exhibits, Financial Statement Schedules.

SIGNATURES

Pursuant to the requirements of Section 13 or 15(d) of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.

Date: March 28, 201930, 2020