That'd sort of ruin the entire point of creating it in an engine like Unity instead of just using Renpy. The conversation sequences need to feel alive by having actual movement in the frame, even if it's just tiny, little details
Yes, it would slightly increase performance to not have it render the 3d elements for that particular 2d screen, but since you are viewing just an 2d overlay, performance doesn't matter since there's no stutter. At that point, the only concern is straining your PC when it doesn't need to, but a modern machine can handle that. The other 2d overlays in the game being viewed on top of the rendered 3d models allow for smooth transitions between menus and the game, instead of having to load the world every time the menu is exited. Yes, it's possible to minmax little things like that to max out performance, but at that point it's just a distraction and my time is much better spent on more performance increasing things like better occlusion culling and enabling/disabling of characters (who are the big performance hit atm because I suck at 3d modelling)
All that said, better options for graphic settings are definitely coming soon! Should hopefully make things run a bit smoother on slower machines, and I do appreciate the input