Exhibit 15

July 29, 2016

Securities and Exchange Commission

100 F Street, NE

Washington, D.C. 20549

RE: Alcoa Inc.

Commissioners:

We are aware that our reports dated May 5, 2016 and July 29, 2016 on our reviews of interim financial information of Alcoa Inc. and its subsidiaries (Alcoa) for the three-month periods ended March 31, 2016 and 2015 and six-month periods ended June 30, 2016 and 2015 and included in Alcoa’s quarterly reports on Form 10-Q for the quarters ended March 31, 2016 and June 30, 2016 are incorporated by reference in its Registration Statement on Form S-8 dated July 29, 2016.

Very truly yours,

/s/ PricewaterhouseCoopers LLP

PricewaterhouseCoopers LLP

Pittsburgh, Pennsylvania