You can still file your 2016 taxes even if you didn't file your 2015. You will need to use your 2016 forms and fill out your return, when you are ready to e-file, you will need to put 0 for your last years AGI since no return was filed.
https://ttlc.intuit.com/replies/4231698
If you still want to file your 2015 taxes you can. TurboTax Online is no longer available, but the CD/Download version can be purchased here: Prior
year TurboTax Products