That actually sounds just about right for total plays, and the NFL average. Even in real life, like in M15 as well, depending on how the game is played (playcalling overall), the numbers will vary.
I certainly encourage you to try out different settings though. Might work better for you. For me and how I play, or at least so far how the cpu has played against me, 15 mins and a 15 sec runoff is just about right.. as it was in M25.