Welcome to group rides, the group I ride with isn't that fast, maybe average 18mph at best, in the rides I go on, but wow is it a humbling experience. I get to see and learn roads I'd never see on my own, and push myself as hard as I can do to catch up with the group. I'd say just keep going to the rides, they may have been going faster than advertised that day just to pick on the n00bs, I'm sure it varies.