Unfortunately, the TurboTax Online 2015 servers have been shut down and the data has been deleted.

However, you can login to the CRA’s My Account service and they will have the information from your 2015 return available. https://www.canada.ca/en/revenue-agency/services/e-services/e-services-individuals/account-individua...

If you have TurboTax Live Assist & Review, here is how to talk to a Tax Expert: https://turbotax.community.intuit.ca/replies/3456106