on what server is your ICM account?
i am on live2 an there is a lot of slippage, live 15 is a little bid better.
Slippage depends from many things. Most important factors are usually the distance between your location and the trade server, internet speed and of course how quick/slow the broker executes your trades. I would suggest that you check how long it takes to executes orders on your account (everything up to 250ms is ok) and then get in touch with the broker to find a solution.
I hope this helps.