Just out of curiosity, I tested the affects of Occlusion Culling on memory usage (system, private, working, commit, GPU) and needless to say, on/off seems to have no effect on memory usage, so the game is clearly not releasing the occluded data from memory; here are some screen shots--the highlighted row in task manager is ffxiv.exe. (ignore the crazy fluctuations in Afterburner, they were caused by tabbing around)

Enabled (OC on)
http://i.imgur.com/xUg8ntu.jpg

Disabled (OC off)
http://i.imgur.com/oBIMXCe.jpg

Granted, I am not a computer science major, but I am quite sure this proves it is not a memory-related issue.