runners have a much better stopping speed than bicycles, and also don't have sharp metal or carbon fiber frames that can hurt pedestrians :)

Also 15 mph is a sub 4:20 mile, and for most people will be pretty close to a flat out sprint. Not super adviseable on sidewalks either. Most joggers will be going half that speed.

walking, 3mph

running at an 9 min mile 6.5mph