OK, played a game at 14 minutes, accelerated clock threshold 15 seconds... way too many plays. 164 snaps is a fairly offensive game in which both QBs were hot. I'm getting off approximately 2.6 plays per minute when the accelerated clock is active, 3 when it's not... now there's a addendum to the last two minutes...
In the first half, when I had the ball a good portion of the time, 6 plays were run. In the second half, when my opponent was trying to catch up in the final 2, 12 plays were run. So the idea that we want to minimize the percentage of the game that the last 2 minutes represents is definitely valid, because it's too unpredictable and can throw stats off quite a bit.
Now, doing the math, with threshold at 15, the appropriate quarter length seems to be around 10-11 minutes. That means that the time spent without accelerated clock will represent around 10% of your game. I'd rather see that lower, so I'm going to play my next franchise game with the threshold set to 20 seconds and see what kind of numbers that gets me.