Reducing Lag or Crashing

I'd like to reccomend something that most players would not like, but will be necessary for the server to not go down because of crashing.

I mean reducing how many bosses donors can spawn in a certain timespan, since:
-lag is increased by mobs spawning. (i.e cube god spawns lots of mobs)
-lag is increased by players dying. (o3 makes lots of players die if there are no Knights who can stun.)
-lag is increased by many people in the arena at once. (make less people be able to enter arena)
I know this, because the server runs mostly smooth, without the donors spawning in mobs. For example:
LeDragon spawns arena mobs most of the time, since people tell him to. He increases lag, obviously.
When he is not on, and noone is spawning mobs, it's smooth.
OR: you could make a time for donors to be able to spawn (2 hours maximum) and turn it into a rule, write it down in the rules, and end the lag spree. Just my idea. :d Cheers!