problem with lag? does "destroy" really get rid of the npc?

[johny023]

i've made a minigame to add into my offline game... and in the minigame you must defend the castle from waves of monsters, after a few waves it starts to lag and after a few more.. it gets to the point where i can't even move, and it eventually gets so bad graal just closes for no reason. in the earlier levels more monsters spawn, it was working just fine with 5-10 spawning at once but after a few waves i can't even spawn 2 without it lagging really bad. so i thought maybe it's just that wave that makes it lag so i pressed F4 skipped to that wave and set everything to be the same way it was before, it worked fine? no lag at all? then i thought.. maybe the "destroy" trigger doesn't get rid of the npc.. maybe it only hides it and stops it from doing anything...

for each wave of monsters i have a npc that uses the putnpc trigger and when the npc dies i used the destroy trigger to get rid of it.
can someone tell me why it lags? and how to fix it?

sorry if i put this in the wrong place not sure where to put it.