Can I still e-file a 2015, 2014, or earlier tax return?
Not if you're filing a personal (1040) return, which has an e-filing window from January to mid-October after the tax year ends.
For example, the 2015 tax year ended on December 31, 2015, so that means personal returns were "e-fileable" in TurboTax from January through mid-October of 2016.
2015 corporate (1120) and partnership (1065) returns are the only prior tax year/entities that can still be e-filed.
Tip: 2015, 2014, and 2013 returns can still be paper-filed using TurboTax. Simply purchase the software and install it on your computer. TurboTax Online is not available for prior-year tax returns.