You can not use TurboTax to file a 2015 tax year or older return. TurboTax only supports their software for the current tax filing season and three years back. Therefore it's absolutely impossible to get the required corrections and updates to the 2015 tax year program or older, and chances are high your return will be wrong without them. TurboTax does not honor the 100% Accuracy guarantee on software more than three years back.