That's what I would do. Playing against the clock is a fundamental part of the NFL game. Any other version deprives that element. And, while I could see less time, I've seen inconclusive overtime games where they take 10 minutes to score so I don't see the point of reducing it if only by 5 minutes if it means the other team is only going to get 30 seconds or so to score. If I can get numbers that say the average time to score is 5 minutes, I could see reducing the total to 10 just to avoid dragging the game out too much, but that's about it.