Exhibit No. 15 August 12, 1999 Securities and Exchange Commission 450 Fifth Street, N.W. Washington, D.C. 20549 Commissioners: We are aware that our report dated August 12, 1999 on our review of interim financial information of UniSource Energy Corporation (the Company) and Tucson Electric Power Company (TEP) for the period ended June 30, 1999 and included in the Company's and TEP's quarterly report on Form 10-Q for the quarter then ended is incorporated by reference in the Company's Registration Statements on Form S-8 (Nos. 333-43765, 333-43767 and 333-43769, 333-53309, 333-53333 and 333-53337), on Form S-3 (No. 333-31043), and on Form S-4 (No. 333-60809) and in Amendment No. 1 to TEP's Registration Statement on Form S-4 (No. 333-64143). Yours very truly, PricewaterhouseCoopers LLP