If you filed using TurboTax Desktop it will be stored on the computer you prepared your return on as a .tax2015 file.
If you used online then follow guide below:
https://ttlc.intuit.com/replies/3301525
If you used neither or can't find the .tax2015 you will need to request transcripts from the IRS.
https://ttlc.intuit.com/replies/3301999
