So, i've tried scenes at my office, i work on a i7 5960 there and it works just fine. Render starts in a few seconds.
At home, at my 2xXeon 2650, the phase takes about 2-3 minutes. Same scene... So i suppose it comes down to this station. I've done all the windows updates, updated drivers in general, nothing works.
Also, interactive mode starts up in a few seconds, so no problem there.
Any more suggestions?