Does it take less space to merge a lot of meshes into a big one?

Hey, I’m working on a projects in which the map is a big mansion. The viewport has gotten incredibly laggy since a few days back, and I figured it’s because of how big the project is and how many different meshes there are in the game. I’m a novice though, so this was only a hypothesis.

I was thinking if it would be reduce the lagging and make it a bit easier on my cpu if I would merge together walls for the different rooms in the mansion.

If no, do you guys who are more experience than me have any idea on what the cause is for the lagging? I do know my ram isn’t the best (I have 8gb), and I have a six-core AMD processor.

Cheers and big thanks for the help!