I've played a couple characters now, engaging in nation-building instead of story missions.
Anyway, I've noticed that once I have >12 folks at Sanctuary, trying to sleep in a bed or wait in a chair or sofa takes EONS. I'm talking about fast-travel-loading-screen amounts of time for 1 hour to pass. It also affects Red Rocket, although no one lives there.
Doesn't seem to affect my other high-population settlements, nor Diamond City (with its crowded streets). So what gives? It it the sheer geographical size of the place (Sanctuary is MASSIVE compared to every other settlement site)? Is it that crackhead "Trashcan Carla" and her [censored] wall-clipping cow-truck?