2nd this comment. I added a weekly group ride to my riding and it really is a different experience. I'm a 17-18mph solo average, but when in the center of a pack I've seen 22-25mph and the weird part is half the time I'm coasting. So lots less energy and faster speeds. It can get intense worrying about who is manoeuvring around you, but you get used to it.

Here is a group ride where I stayed with the alphas for the 1st 10 miles, then settled in with a smaller group. Notice a huge pace difference when I was with the larger group.