It sounds as though the lag is being created simply because there are too many objects on the map. I hope/assume you preload all of your units into the map on map init? (makes a long load time, but gets rid of lag spikes) Possibly add in a trigger as the game goes on to remove all destructables from the map? Then unused buildings, anything the game doesn't need to be played. I ended up having to make a text command -lagless that does all of that at once. It isn't AMAZING, but it helps. Also, if people mass tomes, the item is still on the ground (you can see a little sparkle) and those will create mass lag. I've seen a trigger before on how to clean them up. Make sure you got that, if tomes are involved. Also, a very basic, is to limit the number of triggers running at the same time.
^^Just a few general things that I have had to do in the past month to deal with some problems.
^^Just a few general things that I have had to do in the past month to deal with some problems.