It shouldn't be a 15 yard penalty it should be an ejection and a one game suspension. We've seen to many dudes lose an entire season to that nonsense. For the first 90 years of the game players made tackles from behind without risking a compound fracture to the ball carrier. It's lazy and IMHO mean spirited. Knowing the injury risk to you opponent and doing it anyways shows a complete lack of respect for the opponent and the game itself.