You are comparing apples and oranges.
I would not expect to have the same average. When I had my Jamis Coda, my speed was anywhere between 2-5mph slower than on my carbon road bike. That was not the purpose of that bike. I did do some 25-50 miles on the Coda, but they were not speedy rides... most of the riding I did on that bike was for errands or short fitness rides.