Same thing here. The game was running smoothly on 17.08.2014 suddenly the server got reseted and I lost my character - nevermind, I startet too lot up a bit and quit playing.

The very next day (18.08.2014 I faced the mentioned problem: Server disconnects after EXACTLY 15min. The game freezes and I have to use Ctr-Alt-Delete to get to the desktop.

Edit: As Windows 7 64bit was mentioned <--- Same operation system here
???... wasn´t there an Windows update (17.08) ???