The following has information on getting a copy of your return if you used the Online version for your 2015 return. Any returns prepared with the Desktop software, TurboTax does not have copies of those returns. They are on the computer you used to prepare & file the return.
Access to prior year returns.
You can get a free transcript from the IRS:
How do I get a copy of a return I filed using online TurboTax?
How do I get a copy of a return I prepared using desktop TurboTax?
How to upgrade to PLUS
Note: While you still can, print a copy of your current year tax return and save it as a pdf, too. That way you will have it when you need it for school, a loan, etc. without going through a lot of aggravation to get it.