I'm generally too slow a learner to pick up much in 15 minutes. I'd take for an hour or two if I could afford it.
But at one point, one rink arranged 15 or 20 (?) minute lessons with their coaches, and I took one. I found it useful, because my principle coach didn't speak English well, and there was something I didn't understand that she helped me with.
When another rink made a deal with my ice dance coach for him to push his competitive students to offer 15 minute lessons to people who took his ice dance class, I tried all 3 of his seriously competitive female ice dance students. Shame on me: I switched to one of those students, the one who worked best for me... She was female, so could dance with me, and my then coach was not - and she spoke English better. I didn't know at the time that switching coaches wasn't considered cool. I hope he didn't get mad at her because I switched. (It's not like I was the type of very competitive student he preferred. But he was new to the area, and didn't have enough students to fill his schedule.) But it showed me how much difference it can make to find a coach who works well for me. She wasn't the best ice dancer of the group, but she communicated better with me, and was able to adapt to my learning and movement style best.
I would take 2 or 3 of those 15 minute lessons in a row (I think), so I really took 30 or 45 minute lessons from her.
I think that if a coach arranges his/her own lessons, it wastes his/her time too much to arrange 15 minute lessons. But if the rink does the arrangements, it can make sense for the coach. It might also make sense for the coach if an ice session doesn't have quite enough minutes to fit another 30 minute lesson with someone.
I think a lot depends on how much money and time you have, and whether you have found the coach yet who teaches the way you want.