If you completed the 2015 tax return using the online product, you should be able to find it by using this link:
https://ttlc.intuit.com/community/prior-year-return/help/how-do-i-access-my-prior-year-return/00/270...
If the return was not completed, it is too late to complete it now because TurboTax no longer supports tax year 2015. It is also too late to get a refund on a 2015 tax return. It had to be filed within 3 years of the original filing date to be eligible for a refund.
