You will need to include it on your 2015 tax return. If you already filed your 2015 tax return, then you will need to amend it, in order to add the form. The return can be filed using the 2015 software and the instructions to file are different depending on which version of Turbo Tax you had. Please view the Turbo tax FAQ below for more information.
https://ttlc.intuit.com/replies/3288565