When there's a rule of six in place I don't think the optics of groups of 15 cyclists riding about the place is favourable. Joe Public isn't going to understand that British Cycling affiliated clubs, with leaders etc are able to have up to 15 in a ride and in all honesty it's hard to see why the risk is different for a BC affiliated club ride of 15 people and a group of 15 mates meeting up for a ride.
This feels like BC possibly stretching the definition of organised sport and I can't see that it will enamour cyclists to the friendly motorists and members of the public.