Since you haven't filed your 2015 tax return you can note that in your 2016 return.
If you didn't file a 2015 tax return with the IRS, just tell us you didn’t file last year when we ask you. But if you’ve already entered a number for your AGI, manually enter 0 instead.
You can complete your 2015 tax return by purchasing and downloading the software here: prior year returns. Make sure you choose the correct year.
Please see the following TurboTax FAQ for more information. https://ttlc.intuit.com/replies/3301770