The TurboTax online editions are only for tax year 2016.
To complete a tax return for tax year 2015 using TurboTax you will need to purchase and download one of the 2015 desktop editions from this website - https://turbotax.intuit.com/personal-taxes/past-years-products/
A tax year 2015 return can only be printed and mailed, it cannot be e-filed.