The American Opportunity Credit can only be claimed 4 times for the same student. It doesn't matter who claimed it. So if your parents claimed it 4 times for you, you cannot claim it. But if 2015 was the only time they claimed it for you, you can claim it for 2016 if you meet the other requirements.
(If your parents ever claimed the Hope credit for you, that counts the same as claiming the American Opportunity Credit. The Hope credit was replaced by the American Opportunity Credit starting in 2009.)
