Very cool indeed! I recently picked up that 15mm Sigma F/2.8 fisheye and it is a treat to use for sure!
His biggest stroke of luck was that white ceiling. Had it been any other colour he would have been basically done before he started. The fact that he was using a pair of Ranger S version heads that are 2400 W/s each was a huge help too!
If I was him, I would have knelt down and lowered the angle to reduce the amount of the ceiling showing. Obviously he did some cropping and it turned out damn nice, but I think that this would have improved it.