Even if we ignore freeways and such, a 15 minute drive at 30 mph is about 7 miles, which is a circle containing 176 square miles - or the entirety of the city of New Orleans or Denver.
A 15 minute walk is about a mile, so that's a 3.14159 sq mile circle - that's a small town or a neighborhood or two.
As much as I love going to bat for New Orleans, I will point out that people drive to Metairie all the time for things. The eastern part of New Orleans is also very spread out. (It's also not the 24/7 city it was before the pandemic.) A better comparison would be the towns on the Northshore.
A 15 minute walk is about a mile, so that's a 3.14159 sq mile circle - that's a small town or a neighborhood or two.