I think I’m not slow but this time of year only average about 17 on my 15 mile commute to work
I used to make an effort to train a little more rather than just ride and got much faster 22 average
But this year I can’t be bothered
Holding the bars in the middle and adopting a mild tuck position makes a huge difference to the drag on a mountain bike, I can generally go up one gear by doing so.