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.

Dutch cities are way quieter and more peaceful than American cities. This is because cars are loud.