I have the same problem! It is not easy for me to run a slower pace. I feel like my form breaks down when I go that slow. It actually hurts more. I have gotten the pace to slow down to about 10 mm, but that is the best I can do.

One of the "experts" on this board told me that I was not imagining that, that your form is actually better when you run faster because you recruit more muscles.

They suggested that I would be better off running my normal pace, and taking walk breaks. I did that on last week's long run, pretending that I was walking every other water station at a race. I stashed water on my route( it was very hot), and took a short walk break about every 15 mins to drink.

It seemed to work just fine.