Since you both are new to your bicycles, this may get better, espsecially with a little encouragement. (Bladders are their own issue, though.) It might not I'd go on a couple more rides and sort of make a deal of them going a little faster with less rest stop time ("let's see if we can go a little further before the next stop") in a positive way.
SOme folks really are take-it-easy riders, though.

Now, there are ways to equalize things. Do you still have that old bike? Then you're working harder. Another thing I do is sprint to the rest stop and for another minute beyond, and then back. I've gotten an interval in, my rest is two minutes shorter, and I *want* a rest :-) I just say I'm feeling hyperactive and I'll be there in a minute or two... wear that jacket that acts like a parachute... (the converse of this is that if I'm the weaker in the group I make sure to *coast* inot the rest stop even if everybody else sprints and don't start at the back!)