A 15-minute neighborhood sounds like something out of a guidebook tour: how to see the highlights of Le Marais in Paris in 15 minutes or less. But it’s the newest flavor in urban planning: a city composed of small districts that include all the key services for residents within a short walk. Though the concept, dubbed the “15-minute city,” is of recent vintage, it gained traction during the pandemic lockdowns, when advocates observed that the vast reduction in activity created more “human-centric” neighborhoods, with residents exploring their local streets and availing themselves of nearby services that they might once have...