So this weekend was my first time going in the summer and I'd totally forgotten about the 15's! They're apparently such a regular staple in Disney around this time that they had CM's in the parks in outfits I'd never seen before - green shirts with little Brazil flag logos under the name tags and possibly on the sleeves too, I can't remember. That was kind of neat! I've seen people who have tags listing the languages they speak, but I've never seen CMs that were so obviously out there to help with a specific language. (It's also possible these were strategically placed tour guides also wearing Disney-like name tags, I guess!). For the most part the groups I saw were doing their own thing without incident, except one group at Splash Mountain. The CMs were begging them to keep moving, get out of the way of the queue (they were scanning at the FP+ entrance and then not moving along, all of them seemed to be waiting for friends further back in the group), to put their shirts back on, among other things.
Then once on the ride they were clapping and singing (not singing along to the ride music, singing something totally different) together across multiple boats. It was really weird to be riding up the hill to the big drop & have the 5 boats behind me clapping & drowning out the ride music!
I still think the cheer/choir groups are significantly more annoying because they cheer and clap and sing non-stop. I can deal with it for 2 minutes on Splash Mountain lol, but I can't handle it for 45 minutes in line.