A lot of mods change the precombined meshes and break them, usually without even needing to touch them. I know that LOOT always sorts this as one of the first but this way it rarely helps, especially for heavy mod builds. I personally recommend you to load this mod as one of the lasts. So far the only fix is by installing a mod named Boston FPS Fix. If you want more infos on how exactly this works and why we need it. Bethesda already used those precombined meshes by default but they are not as optimized as they could be plus a lot of mods break those meshes and this can cause horrible FPS drops. Areas around Bunker Hill often had 30-40FPS for me but after this fix it was 60+. This improves the performance inside cities by a A LOT. That is why they created a system called precombined meshes.

The whole game has been build with a help, because Bethesda knew that the engine can’t handle the bigger cities just like that. We are having a nice stroll inside Boston and then, BOOM, the FPS drops to 30FPS and of course exactly at this moments we get picked up by raiders and mutants. Precombined Meshes – Fix Low FPS Inside Big Cities Like Boston

Don’t Use Ultra Godrays – For Pre GTX 1000er Series GPUs.

Disable Weapon Debris PhysX – Fix Weird 1FPS Drops.

Reduce fDirShadowDistance – Better FPS in Some Areas Inside Boston (Financial District).

Use Load Accelerator – For HYPER Fast Loading Screens!.

Precombined Meshes – Fix Low FPS Inside Big Cities Like Boston.

Fallout 4 faster loading screens mod