on most good sites, an additional 15 hives is neither here nor there.
the positioning makes me think...
if the hives are facing south, why would someone want to put them behind a fence. They would be better at least a few feet from the fence, or in a different orientation.
Whether the bees are a few yards from the fence, or a hundred yards from the fence, it makes little difference.
if your friends hives are being robbed, then the entrances should be closed down (against wasps too) to suit the size of the colony, particularly at this time of year.
This would be no different as having a large colony in an apiary with a handful of fed NUC's. If the doors are too big, the large colony will try and rob the NUC's.
Bees will not rob colonys because they belong to someone else.
A lot of people are having poor results this half of the summer. After July, my honey crop has plummeted.
your friend wants to lighten up and be a little less territorial (very common amongst beekeepers).
Try and talk to the semi-commercial, and try and be good neighbours..