For 2015, you will need to use a version of the 2015 TurboTax software. The way to get that is to purchase a download/CD version as it is no longer available online. For your 2016 taxes, you can use the online version. Each return is processed using the software (with appropriate tax laws) for their respective year.
Prior Year Turbo Tax Software (2015) Prior
Year TurboTax Products
Online 2016 versions can be found
at this link TurboTax
Online Versions
TurboTax
2016 CD/Download versions and pricing can be found here
TurboTax CD/Download Versions
