A 15 minute city is where everything is available to you within 15 minutes walking, biking, or public transit.
I know Mexico city fits this bill. Playa del carmen as well.
PDC I’d rather avoid. A bit too party tourism, dangerous I found.
Vallarta I’ve been too and almost fits. I enjoyed there.
Guanajuato is lovely and fits the bill here, as long as you don’t mind going up and down lots of stairs haha!