Does anyone have experience? Well, most of human history was that way. Up until the industrial revolution many towns were based on how far one could walk.
This changed with the advent of motorized transportation and cities began to spread out, suburbs became a thing. But even so, it took a century for big cities to become impractical to live in without personal transportation. Indeed there are still places where one can live that way.
My problem with planning a 15 minute city is the planning part. The changes mentioned above happened organically, the citizens made the change, not the government.
My home town of Cleveland had that history and is slowly starting to return to it's history. Particularly in the 70s and 80s many stores that surrounded Public Square closed and became offices, beginning in the 2000s many of these offices are being turned into apartments. One local grocery chain has turned an old bank into a grocery store, other stores are opening as well. But this change started because downtown workers got tired of commuting from the suburbs. There's always been restaurants and delis, go to the original Slymans and get there early.