There will still be plenty of big plays, when a db is burned he is burned, nothing left to tackle. College still has plenty of big plays despite the max penalty of 15 yards.
I would propose splitting the difference between college and pros. Still a spot foul but the max penalty is 1/2 way to the goal line. That way a PI in a hail mary from mid-field would result in the ball at the 25 rather than the 1.