If you used TurboTax CD/Download in 2015:
You will need to find the 2015 files on your computer or wherever you keep your backup files. Search for files with the .tt15 extension, or check your documents folder. By default, TurboTax saves files to this location (though it may be different on your PC): C:\Users\Your_Name\Documents\TurboTax\2015
You can download previous versions of TurboTax/CD Download here to reinstall the software: https://turbotax.community.intuit.ca/replies/3001486
If you used TurboTax Online in 2015:
The 2015 servers (and those of earlier tax years) have been shut down and the data has been deleted. If you didn’t save a PDF copy of your 2015 return, then you can look up the information via the CRA: https://turbotax.community.intuit.ca/replies/2647704
Please be aware that TurboTax doesn’t support REFILE on returns from years prior to 2017. To make changes to your 2015 return, please see this CRA webpage: https://www.canada.ca/en/revenue-agency/services/tax/individuals/topics/about-your-tax-return/change...