testfor enteties makes much lag

i was making a snowboad/minecart minigame w/ stunts and lots of commandblocks.
But when i almost was done every minecart was staying in mid air.
I pressed shift + f3 and the unknown part of the circle was: 76%.
i used powered rail to make the jump and i used a counter between the landing and the jump to calculate how high it should jump. I think all the testfor @e commandblocks made the error.
After many reloggs the world got removed somehow.