Exhibit 15 Tucson Electric Power Company 220 West Sixth Street Tucson, Arizona 85701 We have made a review, in accordance with standards established by the American Institute of Certified Public Accountants, of the unaudited interim financial information of Tucson Electric Power Company and subsidiaries (the Company) for the three- month and six-month periods ended June 30, 1996 and 1995, as indicated in our report dated July 26, 1996; because we did not perform an audit, we expressed no opinion on that information. We are aware that our report referred to above, which is included in your Quarterly Report on Form 10-Q for the quarter ended June 30, 1996, is incorporated by reference in Post-Effective Amendment No. 1 to Registration Statement No. 33- 55732 of the Company on Form S-3, Registration Statement No. 33- 58173 of UniSource Energy Corporation on Form S-4, and Registration Statements No. 33-56523, No. 33-57233 and No. 33- 57231 of the Company on Form S-8. We are also aware that the aforementioned report, pursuant to Rule 436(c) under the Securities Act of 1933, is not considered a part of the Registration Statement prepared or certified by an accountant or a report prepared or certified by an accountant within the meaning of Sections 7 and 11 of that Act. DELOITTE & TOUCHE LLP Tucson, Arizona August 8, 1996