Vehicles that move faster than pedestrians should go on the road, like bicycles do. As a bike rider, its a vastly superior option that going on the sidewalk.
And to be clear 'bike lane' != road shoulder with a bike painted on it. A bike lane should have at least some amount of separation from the road in the same way that sidewalks are separated.
I'm hopeful that the popularity of scooters speeds up the adoption of medium speed lanes.
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