I actually played once with the spawn rate set to 50 (and I regularly do so for testing purposes). I even turned on surrounded start with a random scenario (an “in the wild” start).
However, I set the monster speed down to 50% (but doubled their resilience), so that I can at least survive the first few minutes.
Yeah, they demolished a lot of houses, but for me that was just part of the challenge.
My character set up her base at a cabin in the woods and survived over 2 years (and is still alive, but I moved on to a different character and game version and never got back to her).
She usually would pick Zombies off one by one, which did work great, especially with the slower movement speed for the monsters.
However, she never did go into any labs (she never found one, they were really rare at that time).
From my testing worlds I know that they are overflowing with monsters, the same as with Necropolis, so… better keep away from them if you (and your computer - the lag is horrendous) want to live.