If
@chrizeren checks in again someday, it's worth trying
Sim Settlements 2. Stability is far, far better than Sim Settlements 1. Everything runs way faster now, tons of new stuff fans have requested for years but were impossible to implement on SS1 is now here on SS2 plus epic story. Conqueror will be remade for Sim Settlements 2. We're looking at a golden age for Fallout 4.
Things are so much faster that I can create a plot with over a hundred spawns with most of them being dynamic(formlist &/or external plugin, both of which could slow things down on plots back on SS1) and it'll set up faster in game now than simple plots did back on SS1. The workflow for plot creation is much better now so it's feasible to have some more complexity to it.
Perhaps if he has not enough VRAM / generally underpowered GPU or an integrated GPU(which generally just use system RAM for all of their "VRAM")?
FO4 for me tends to use 7 or 8GB but I have lots of VRAM and 32GB system RAM. VRAM usage tends to be at around 10-11GB if I'm at 4K but I have tons of texture packs(180GB Fallout 4 install). But yeah FO4 seems to manage resources well enough for me, even with 500 active plugins.
32GB RAM should be more than enough, and if DDR4 should easily be fast enough. Depending on overall specs you may see bigger gains from upgrading GPU or CPU. Or reducing resolution. Do you have an SSD? If playing FO4 on an HDD, it's worth moving it to an SSD.
Probably worth it to run thorough AV scans in case of any malware, and might be worth it to consider a clean install of Windows if there's also a lot of OS problems happening. I would try running RAM testers to see if the current RAM is faulty.