Enemies Spawn Too Frequently and are Generally Too OP

The enemy zombies in the game (the TV ones especially) spawn far too frequently and always zerg rush me every time I get near them. This usually would be a fun diversion from generally exploring if they actually disappeared when being vanquished. However, often when I'm trying to collect a gnome, or doing some sort of Gnomolith puzzle, they spawn and start attacking me! I vanquish them, then go on to continue working on the puzzle. However, 2 seconds later (this is an exaggeration) they come in and start attacking me again, turning what should be a fun side-quest into monotonous bull-honky.  In addition, they seem to use their strongest attacks first, and try to get in every last hit that they possibly can before being vanquished and resurrected in a short amount of time. This not only extends to otherwise standard zombies but also to zombie heroes, TV Head zombies, and even the bosses. I often find myself running then being killed in seconds thanks to the enemies' sniper-like aim. I understand that running and jumping is often an easy way to get away from other players in PvP mode, but in story mode, I want to take my time and actually do side-quests without being attacked frequently. Is there some way I could turn down the difficulty so they spawn less frequently, or not have to deal with them at all when doing side-quests? Thanks for taking the time to read this!