I subscribed and tested your map, and it's a good one! well done! But there are others who are saying that it is "laggy" and I agree with them.

I do disagree with them on the fact that it's "too many zombies" I think the zombies are the problem though. Not the number of them, (although I guess it could have to do with spawnrate also) but the fact that the majority of zombies spawn in any available clothes and skins. You should create zombie nodes that spawn with "environment specific" clothing and drops and limit each individual zombie in certain areas to wear/drop specific things. If you load every zombie up with almost every available clothing and drop, then horde them up, it overloads the map and causes for poor optimization.

If you want to leave the zombies the way they are, then yes, I would probably suggest lowering the number of zombies on the map, and make them stronger instead.

Good luck!