From what I’ve tested, this doesn’t happen at all in the character selection/creation, nor in the login screen. It happens a bit LESS in non-crowded areas (but can certainly still happen, as it has happened to me in a near-empty Darkshore and Nazmir both). It happens to me all the time in Orgrimmar. When the frames hit 0, my memory usage spikes to absurd amounts, and other applications begin freezing as well.
This did not occur in 8.2.5, and DID occur in the 8.3 PTR from its initial testing periods up to right now.