Well... RAM always helps game performance, the more RAM you have, the better the game and all your applications will run. When it comes to gaming: More RAM (memory), a stronger GPU (graphics card), a stronger CPU (processor) and a faster hard drive helps with game performance.
The more things that the game needs to process, the more it will demand from your computer. From my experience, larger and older saves, larger lots, lots of sims wanting to do things, lots of cc and mods makes your game demand more and will affect your loading times and performance. But how much of these things that will affect specific parts of the game I don't know.
I always recommend having 16 GB RAM for computers these days.
From my experience from upgrading my computer and playing sims4 over 8 years:
Better and faster hard drive - Helps with loading times.
Better and faster graphics card -Helps with how well the game runs, especially rendering lots and also framerate. Although bear in mind that the game does not use this effectively and will still lag sometimes no matter how powerful your GPU is.
More RAM - Helps with game performance overall and handling the things I listed that the game needs to process.
Better CPU - Helps a lot with how well the game runs, and simulation lag.
