> 25 and 50 minutes are more natural than 20 minutes from decimal POV.
Not really. Quarter hours and half hours are natural units. This is true no matter how many minutes we divide an hour into. There's nothing special about "25" when you're building up from 1. 25 is only special when you're splitting up 100, and nothing uses 100-minute blocks so that doesn't happen.
> I'd say the fact that 15, 20 and 30 fit nicely into an hour plays a role in their popularity
I'm skeptical for 20. I think 20 being a nice round number plays a much bigger factor here. If hours were 65 minutes I think you'd see just as much use of "20 minutes".
If 20 minutes was used because it's round, then we would expect 40 minutes to be used commonly. I'd say 45 minutes is used much more often.
As for non-time-related units, I hear 25 deko more often than 20 deko when buying food. I don't think there's really a distinction between building up and down. When you're talking about 250 meters do you build up from meters or down from kilometers? I think both.
I'd say the fact that 15, 20 and 30 fit nicely into an hour plays a role in their popularity, even if you don't realize you use them for that reason.