Many of the minimum connection times come from simpler days, when a plane arrived and you could zip right over to the next flight. Planes were on time way more, boarding was easier, and all that stuff.

As they started expanding airports, it was no longer a few minute walk from one end of the terminal to the other, you started to have to go out and back through security for example, and they never updated the connection times.

I can't possibly believe 15 minutes is a legal connection time at any airport. Even if the two gates are right next to each other, there's virtually no chance your luggage will make it.

Saying all that, travelers need to take some responsibility for it too. If you know you have to change planes and you know you have 20 minutes to do so, you need to rearrange your flight times or airports or whatever to something more reasonable.