Y'all might be imagining NYC levels of density and, while that's important, is definitely several steps further than what's needed to make America not terrible. Something like rowhouses or even 4-plexes would be an improvement, and that would, at max, only add 50-100 more people to the average city block.

If you already live in a neighborhood, you would really only be interacting with your neighbors as you do now. It's not as if your entire city is going to be in the same 15 minute stretch.