I can't read the png that well, but if it really says: 17 hr 45 mins, on 2 threads, 2 GPU, and still only at a 2.55 samples/pixel quality level then there is something 'wrong'.

Is the Eff (iciency) really just 15%? Then your lighting levels are far too low (your histogram suggests that too), Eff should be 100% at least, preferrably 200-500%. Just turn up the lights in the Light tab. The ISO value seems a bit low (50?) as well. Then you're combining low lighting with low ISO (insentive film), that will take long lighting / render times indeed. 

Since the renderer was apparently paused for the screenshot, I cant see a samples/second value. I do see its a say 2500x2000 image, why not make a far smaller testrun first (500x400 will render 25 times faster, turning days into hours).

Note that 500 s/p is considered somewhat reasonable draft while you need 2000 - 4000 for a serious quality result. The larger your image, the more you're into printing, the higher your quality requirement will be too.

- - - - - 

Usually I'm wrong. But to be effective and efficient, I don't need to be correct or accurate.

visit www.aRtBeeWeb.nl (works) or Missing Manuals (tutorials & reviews) - both need an update though