I've had worse, LOL!
And besides, my dog is almost 2-1/2 and weighs less than that! Have some fun with ignorant comments.....I'd say "Oh yeah, she's no Rottopotomus! She's a ROCKET, isn't she just great?"
There's a lot of stuff you have to just let wash over your head...don't hold onto it, because it'll just make you crazy and ruin the good time you should be having with your dog.
As for the class size, 23 dogs is a HUGE class, even with an assistant. I don't think I'd be too happy with a class that big. We might have 10-12 dogs in Chili's class at most, and most of the time we have additional help as well. There are quite a few very advanced people in the class, some of whom are trainers and others who just know their stuff, so we frequently break off into groups of 3 and work "stations". The instructor makes sure each group has a mix of advanced to novice, so there's more one-on-one time with people of a trained eye and the ability to guide others correctly. On those occasions, the instructor will go from group to group and give her input also. It actually works really well.