If you are amending the 2015 return, it would be in your best interest to follow the program interview to start the amended tax return, Form 1040X. See this TurboTax support FAQ on amending a 2015 return using the desktop editions - https://ttlc.intuit.com/questions/2693843-how-do-i-amend-a-2015-return-in-the-turbotax-cd-download-s...
In Forms mode, if you have not started an amended return, it will not be shown on the left side of the Forms mode screen. Click on Open Form at the top left of the screen. Type in 1040X. Click on the option shown, Form 1040X: Amended Tax Return to open
