Welcome to the forum and the madness that is the 15-22.
I don't have a SlideFire set as I live in UK and can't get one for the love of money.
However, there are many posts on here regarding the slidefire and the muzzle adapter.
From what I have read the muzzle device is supposed to help increase the blowback of the system and as a result it apparently makes it work much better, that said, a sound moderator also adds more blow back pressure so could help if you have one.
There are also members who have posted that the adapter has made no difference to how the slidefire works compared to the regular flash hider.
I am sure that someone who owns one will jump in with more comments and feedback on this point.
To fit the adapter, I will simply advise the following, clamp the BARREL not the UPPER. Unlike a true AR, the lugs are plastic not metal.
The barrel if not clamped correctly could spin in the upper and chew off the 2 lugs that hold it in place. This would ruin the barrel and the upper.
Again I am sure once more that others will jump in with advice but suffice to say, use clamps on the barrel, make or buy them from wood or alloy, some have said it was a nightmare taking the muzzle device off, mine came off pretty easy so I'm guessing there is lots of difference from one to another.
Also, if you use the search function on the forum you should be able to finds loads of hints tips and pointers.
Hope that helps some.