Spamming /fill on a command block gives a huge spike lag

I'm trying to make a spleef arena using /fill 1 1 1 2 2 2 wool
and put it into a redstone circuit.

So that when i destroy the wool it will automatically be replaced but after doing this it gives me about 1-5fps only.

Hardware:
1GB Ram
1.6GHZ Dual Core Processor
305MB Video Card