This is the result of congestion, this is one of the few games where the developers have done any kind of throttling to at very least keep the core servers up, otherwise we'd have log-in server crashes, regular serer crashes, and instance server crashes constantly occurring, and they cant collect telemetry data from server that crash/go offline.

While players are not pleased, that they CAN log in and stay logged in...I'm guessing they would prefer server crashes onl all fronts every 15 mins. /shrug