I work on a large rails codebase as well but within a docker container doing emulation because ARM. How does RubyMine perform then? Last time I tried it felt sluggish.
Do you mean the search itself or other parts? Quite possible that I've become accustomed to the parts that are slower being used to IDEA. e.g. I accept the 'indexing' operation sometimes on startup or the now rare garbage collection pauses.