If that's a real Green Slimer, and it probably is, I think you'll see good and rapid growth from it, as long as your params are stable. I really think a lot of these slow growing slimers are just green staghorn like acros sold as slimers.
A real slimer will fill the tank with slime if you touch it and your hands will smell for the rest of the day.
If for some reason you have to remove a slimer from the tank for any length of time and you happen to have a wife she will ask you what that horrible smell is.
Any green coral that does not exhibit these tendencies is not a real slimer, IMO, -OR- I don't have a slimer but some other green coral that is probably adapted to living out of the water (low tide) on a regular basis.