[titanomachy]

By "dive for 15m" you mean "swim 15 horizontal metres while underwater", right? Diving 15m deep is a pretty elite skill.

[JackCh]

He almost certainly means 15 meters horizontally. Besides most hobby free divers not going to 15 meters very often, I'd wager 15+ meter deep pools are pretty uncommon even in Iceland.

[OscarCunningham]

Or perhaps "dive into the water from 15m above it"?

[titanomachy]

Also a relatively elite skill, though.