Do you need to prepare a 2015 return? Online is only for the current year so you have to buy the Desktop CD/Download program here
https://turbotax.intuit.com/personal-taxes/past-years-products/ Or you can get the blank forms from the IRS and do them by hand. Either way you will have to print and mail prior year returns. And send each year in a separate envelope so the IRS doesn't miss any.
Here are some blank forms & instructions for 2015
1040
https://www.irs.gov/pub/irs-prior/f1040--2015.pdf Instructions
https://www.irs.gov/pub/irs-prior/i1040gi--2015.pdf 1040A
https://www.irs.gov/pub/irs-prior/f1040a--2015.pdf Instructions
https://www.irs.gov/pub/irs-prior/i1040a--2015.pdf 1040EZ
https://www.irs.gov/pub/irs-prior/f1040ez--2015.pdf Instructions
https://www.irs.gov/pub/irs-prior/i1040ez--2015.pdf 2015 Tax Tables
https://www.irs.gov/pub/irs-prior/i1040tt--2015.pdf Publication 17 Tax Guide for 2015
https://www.irs.gov/pub/irs-prior/p17--2015.pdf
