2D game, how to display just background objects at a lower render resolution?

Context:

I'm working on a 2D, sidescrolling "metroidvania" style game. The environments are made using many pieces of 2D art arranged in perspective.

Generally speaking, my scenes that contain levels are structured using a "background object", which has every art element designated to be in the background childed to it, and a "foreground object" which has the same.

My game is very graphically dense and so performance is becoming an issue on lower end hardware, so I'm looking for ways to free up head room. In my settings I've made it possible for users to change the game's overall rendering resolution, and lowering it carries a significant increase in frames.

Because of this, I thought a smart optimization may be to find some way to lower the render resolution of only the background and perhaps only the foreground, leaving the characters and other close up objects able to render at a higher res.

I'm an artist and designer first, and I've been doing this mostly alone, self taught. I have some gaps in knowledge. Is there some (reasonably doable) way I could implement this concept as outlined above, and if so, how?