Moderate could mean just about anything. If they're serious roadies, it'll be fast, like maybe 17-18. Even if it's described as a no-drop ride, there's a chance you'll be left behind. Don't be afraid to call any listed phone number and ask questions. I've been on rides where I felt I was clearly out of my league. I lived to find other rides. Just make sure you know how to get back without the group.
Snobbery is common, but not inescapable. Most people I've ridden with don't care what kind of bike you have. Some people who have thought about putting down another rider or his bike have learned their lesson by having the rider they put down leave them in the dust. Most of us are just glad to have more riders with us.