Yes absolutely, if somebody has some kind of postural problem or a chronic problem for example a plantar fasciitis if you make
him to run at an easy pace for 90 minutes is a lot more stress than do some fast repetitions.
When we run slow the ground contact time is a lot bigger than when we run fast, so running for 90 minutes slow makes
all your problems comes out and maybe the pain comes out if an injurie is present.
Running fast is less stressing , more speed less ground contact time and in general less total time running.
Also body weight can make a huge difference on how easy feels the easy run.