Limiting what pages WordPress queries

I’m looking for a way to limit what pages get queried when certain links are clicked. For instance, in my situation, I have 50 parent pages but about 15000 child pages under the various parent pages. My homepage will have links to all 50 parent pages but I’ve noticed after adding the 15000 child pages that it has slowed wordpress down quite a bit. Is there any way to limit the wordpress search to only the parent pages (and exclude all of the child pages) when the specific link is clicked on the homepage? Would that even help speed up the load time? My though process is that if it only has to search through a 50 page loop for a specific page instead of a 15000 page one, it should help the load time significantly.