Render time abnormally long..

Hi everyone !

I know my build is really old, but before, I was working on a Macbook with these specs : Intel I3, An integrated graphic card (intel HD something), 4Gb of ram.

A Music video of 3-4 minutes with a visualizer a background and some small particle usually took me 2h hours to render.

Now with these specs :

Intel Double Xeon E5620 16 x 2.66 Ghz (24M Cache , 2.66 Ghz)
DDR3 12GB ECC
NVIDIA Quadro K600

That exact video takes 6h ??

I was hoping to work with better/same performance as my old macbook, not worst..

(Im rendering with Media Encoder, and my processor is using 20%-30% of its ressources).

Is there something I can fix ?

Thank you.