If you used TurboTax Online, 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

If you used TurboTax CD/Download in 2015, then the files were saved to your own computer and we don’t have copies of it. Here is some information that may help you find your files if you used TurboTax CD/Download in previous years: https://turbotax.community.intuit.ca/replies/3285180