3900 zombies, each defined as a static mesh component, seems pretty excessive.
You’ll probably want a better way of managing those.
You’ll probably want to use Mass for this, as that’s what it’s for:
Another alternative (used before Mass was available) was to create each entity as a “particle” in Niagara so it can all run on the GPU; it gets only limited interaction with the world that way. It’s used for the beetles in the original 5.0 “not Tomb Rader, we swear!” demo.