Kilo, I don't have the exact "net" reverse trust on a CFM56-7 but I know that an RB211-535 estimates 25-30% net reverse thrust. I doubt the CFM engines can produce substantially more than 30%... or in this case 7,800 lbs (static). Remember that you can only reverse the fan bypass air... and only "at best" 45 degrees in relation to your direction of travel... and then deduct your core thrust... and you are left with about 30%... The "total" reverse thrust also changes with your forward velocity... and is obviously greater at higher velocities... but diminishes as the aircraft is decelerating... Finally, your "window of opportunity" to apply full reverse thrust is relatively small... since you first have to get the "ground" signal for the TR to deploy... then wait for the TR sleeves to travel a certain distance to get the "throttle interlock release"... and then allow the engines to spool up from idle... and be back out of reverse thrust "at least" before reaching 60 kts...
The combination of ground spoilers, reverse thrust and "proper" use of brake application is your best bet at stopping the aircraft... even on contaminated... or as you said "slippery" runways...
Dag