To prepare your 2015 return using TurboTax you need the 2015 Desktop tax software and the return must be mailed in. A prior year return cannot be done online; the Online version is only to prepare the current year’s return. You can go to the following website to purchase and download TurboTax’s 2015 desktop tax software.
http://turbotax.intuit.com/personal-taxes/past-years-products.jsp

Or, You can go to the IRS website to get Prior Year Federal Forms, Instructions & Publications to manually do your returns (enter your form number in the find box)

http://www.irs.gov/app/picklist/list/priorFormPublication.html

If you need to file a State return manually you can go to your State's website for prior year forms to manually fill out & mail.

You can also check a website like Amazon.com for prior year TurboTax software, or search the internet