Tower Unite isn’t too poorly optimized most of the time, and they frequently try to make improvements, but it does have some compatibility issues. By that I mean certain graphics cards (And often integrated graphics) just struggle to do much at all.
Just a very small upgrade in GPU can boost performance a lot, my PC isn’t great at all, and I have a fairly low end GPU, but even with maxed out graphics I can still get around 40 FPS in most areas.
Shadows being on low helps a bunch. I’d recommend making sure you can handle the textures and foliage too. Try experimenting with it a bit till you find what you want.