Each tax year must be filed separately. You can't use the online product to file a 2015 tax return. It is for 2016 only. To file a 2015 tax return using TurboTax, you must buy and download the software and install it on your computer. Here is a link: https://turbotax.intuit.com/personal-taxes/past-years-products/

A 2015 tax return must be printed and mailed. It can't be efiled.