I'm looking for my 2015 tax return?

TurboTax only maintains tax returns for the past seven years, the same retention period as the IRS.  A 2015 tax return is no longer available.

if the iRS sent out a refund and you never got it, you may still be entitled to it. The IRS is holding several billion $s in unclaimed refunds

If you lost your refund check from 2015, you can initiate a refund trace with the IRS. Here’s how:

 call 800-829-1954 using the automated system. however how far you can proceed without some info from that year is unknown
If you filed a married filing jointly return, you’ll need to complete Form 3911, the Taxpayer Statement Regarding Refund.