I was pretty surprised with how clean their crates were when they got here. I don't think either one of them did anything in their crates, though they were both VERY happy to get out once we got to the flat.
My parents dropped them off at about 4pm EST and we got to the flat about noon BST, so yeah, 15 hours is about right.
Oh, and I don't know if the Heathrow ARC has told you anything about picking them up, but the flight got in about 9:30, they supposedly made it to the ARC about 10 (I showed up at 10:15) and we were out the door at 11, so the turnaround time was pretty quick. Officially it can be up to 4 hours, I think, if they've got a lot of animals to process.