That's a very complex scene, Aleks, which is why it took so long.
As the scene complexity increases renders take longer because there are more surfaces to calculate.
Also I assume you are using Ray Tracing or Photon Map or another single pass rendering method. Because this method only sends out a finite number of "photons" or "rays" and there are so many surfaces, mathematically, chances are that one of those hundreds of thousands of surfaces will be missed by the relatively few paths, resulting in missed spots in the render, manifested as white dots.
This is why a multi-pass rendering method (metropolis light transport, preset 20 or 21, I think) is so important. It essentially keeps passing over the same image, and by those mathematical odds (again) by 100 passes all of the surfaces would have been hit and the white spots will be filled in.
And that's it.
tl;dr: Use MLT.
