There is no way he's running out of VRAM or RAM here. That's not an AMD chipset, either.
Try:
Setting the option that turns GraphicsLib OFF.
Lowering Battle Size.
Disable Music.
Disable Sound.
Basically:
1. GraphicsLib still occasionally has shader initialization / other OpenGL issues on certain chipsets / drivers. Usually not nVidia, but there can be exceptions.
2. Battle Size governs a lot of things, but it lowers CPU loads considerably. If that's where you're choking, it'll help.
3. It's always possible that too much stuff's being submitted to the sound drivers or your hardware isn't handling streamed OGG files well and the game's getting choppy as a result. It's unlikely, but it could be happening.
I tried all of it, the only difference was made by the battlesize, which makes sense but playing with such a low battlesize is little fun and I feel like my rig should be easily able to handle it.
Vanilla SS at least ran without lags at battlesize 400.
Does anyone have any idea which mod is heavy on the performance side? If at all possible I'd like to remove as few mods as possibles.
Try to see on the Discord, because you have many mods and on the unofficial discord, some people can point you.
Per exemple for my case, Gladiator Society is very light. Compared to Interstellar Imperium which is a fat mod(but top-tier, so in this case, remove Gladiator for win basically nothing, but this is always better)
After, i have never tried every utility mods than you use but Starship legend+ Nex + Ruthless sector +well, 99% of utility mods available. They can be heavy. So, better to see on the unofficial Discord, they know maybe the cost (and like there are many people).