Modular kits mesh merge tool + clean up

We are creating a level with modular kits such as walls and floors. We run into a problem with having too many draw call. Is there a tool out there that let us click select multiple meshes then combine them also able to uncombine for later editing. I know that Unreal has mesh merge tool but it is doesn’t do mesh cleaning, ie deleting inside faces. Or something that can do optimization during Cook Time: no editor work. Just a cook process plugin that combines assets based on material.