Lowering your settings probably made it worse - this is due to the setting "occlusion culling", which tells the game not to render anything that isn't directly visible. It helps overall performance but means that the game has to quickly load in new stuff all the time when you move around. As a side effect you get this kind of pop-in effect when you run around corners, of which there are many in Ul'dah. Untick "Disable rendering of objects when not visible (Occlusion Culling)" and see if it helps.

If not, then I'd say whatever hard drive or SSD you're storing the game on is performing so badly the game can't load objects quickly enough.