If pedestrians or especially children are present, one should be driving very slowly. 15mph sounds about right. At that speed one is unlikely to kill, since even if a pedestrian "jumps out" (an event that is vanishingly less common than drivers not paying attention), one has enough time to stop.

Most drivers drive too fast. (Me too!) Most drivers have not killed anyone. All drivers who have killed someone, were driving too fast at the time. Many drivers will disagree with me, but they are simply wrong about appropriate speeds, and we will all be safer when robocars are driving for them.