I took a quick look at the stuff which has been falling out of Colonies 15 and 16 today.
The removable tray under Colony 15 had lots of new wax platelets, indicating that they're busy building comb. There were also at least 3 Varroa bodies. This shouldn't be a surprise. Varroa are in all the colonies which I've encountered. This period after swarming has no brood so all the Varroa in the hive are clinging to the bees. Every mite which dies now does so before it can infest a brood cell, which is good news.
While Colony 15 had very little comb in their hive, Colony 16 had lots. Much of this was brood comb from a previous colony. It was beginning to suffer from wax moth and was heavily propolised (brood cells are lined with propolis). After only 16 hours were was a thick mess of dropped comb on the removable tray. There were half a dozen wax moth larvae in various stages of development -- a vigorous swarm doesn't tolerate them. The detritus was so thick that I couldn't tell whether there were any Varroa. I'll have another look in a day or two.
One method of detecting Varroa mites amongst a thick layer of muck is to use Methylated Spirits (a mix of Methanoic and Ethanoic alcohol). This separates the mites from the muck, making them easier to see.
edit 25/05/2019: the flight patterns of colony 16 appeared to be the increasing circles which indicate orientation flights. It's hard to be certain. Individual bees are hard to see -- they are small and dark; they move quickly across a patterned background and there are lots of them.