I think its time for a new pc my dude.

Generally lag would be caused by a slow CPU, or just asking for too much even with a fast CPU.

A lack of RAM would usually just cause the game to crash.

I think the best idea would be for you to tell us what specs your computer has and that will tell us if it should be able to run the mod and at what settings. In windows 10, you can find this by searching "system information" in the search bar. I'm mainly interested in the Processor you have and the Installed Physical Memory. If you're on a different operating system, you can just google how to find out what specs it is.

"the ME dimension takes up most of the mod and is responsible for the majority of the lag"

The dimension itself shouldn't cause any lag when you are in the overworld. If you're referring to all the things in the mod that are only accessible through the dimension (or creative) such as NPCs, scructures, and game mechanics, then that may be the cause of some RAM usage. However, most of the RAM will be used for textures of blocks, items, and entities, as well as the world you are in.

TL;DR: No you can't remove the dimension, nor would it help significantly if you could. Best course of action is to provide your specs.