Yes, yiu are required to file a 2015 8606 reporting the non-deductible contribution. There is a $50 penalty for a missed 8606 but don't pay it unless the IRS sends a bill.
You can get blank 8606 forms for 2015 here:
Thank you sir! So just a clarification, this isn't considered a tax amendment, correct? So instead of amending the actual tax return from 2015, I would just simply mail in the form 8606 from the 2015 tax year, right? Again, thank you so much for replying.
No, you did not reported it incorrectly in order to amend, you did not report it at all so there is nothing to amend - you are not changing anything which is what an amendment does. . You are simply filing an original form late that should have been part of your 2015 tax return.