You can't optimize it. It will be worse with higher pop. The more people you have the higher CPU usage.

As for the crash, without seeing data from your logfile I can't help you.
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=1638396595

Logfile link:
https://drive.google.com/file/d/1WUe2wYhJvW6SkNnDmhu5b4ZzSSC93PuI/view?usp=sharing

More informations:

Map size: Large

Use mods (with "`" were added after started game):
Extended Starage Menagement
Warmer Mild climate
FogOff
Garden (with a stone fence)
Large barn
Better Cheat Mod
Modify Villagers characterisice
Command Post
Bordar's House
Medieval garden
Larger stockpile storage
Town Mansion
Town Pension
Small Burial Ground
Increase Camera Distance
More productive orchards
Adjustable Diseases
Small edible garden
Faster expeditions - no pies
Better Food
Clock Tower
Steel Workshop
More productive animals
Sandbox: Free Materials`
In-game Music Bundle`
Sandbox: Free Resource`
Game settings`
Smaller school

these problems started to arise on oldes save with the 5 mods

Sorry but I only check logfiles sent to email.

And I don't need anything else than log so please follow guide.

Logfile should be after your game crashes, log without crash is useless.

I reloaded this game, the error popped up again so it should be okay.
I sent email with Log file.
although I do not see any information about the error anyway...