That punishment doesn't fit the crime. I have a hard time seeing the Fed add a 5-yard IP foul, though. For an accidental step out of boulds, I wouldn't mind (what I think is) the NFL rule - if an A player steps out of bounds and is the first to touch the pass, consider it incomplete - no yardage lost, the down counts, just like an incomplete pass.
Now, if we determine that someone's trying to gain an unfair advantage, stick them with the 15.