The best place to get your 2015 adjusted gross income (AGI) is from last year's original, unamended tax return. (Make sure you round your AGI up/down to the nearest dollar amount.)
Here is a link to further assist you:
https://ttlc.intuit.com/questions/1900840-how-do-i-find-last-year-s-agi
**You will have to upgrade to Deluxe or Premier to see your last your return.