Loading speed seems to be mostly related to the number of files you have in your Community folder. Not the size of the files themselves. So, large Google Maps addons will slow the sim the most.
And RAM is ok. I’d say if you can afford it, double to 32.
I run MSFS on a Razer Blade 15 Adv. I upgraded the RAM to 32. I do see RAM go past 16G on a few occasions, so for me it’s worth it.