A lot of times you want to describe the purpose of the 15 minutes in some way. When the purpose is described by a noun, the adjective 15-minute can be used. For example:
a 15-minute break
I'm taking the dog for a 15-minute walk.
In Dutch you might multiply the kwartieren, for example to denote 45-minute or 75-minute periods (30- and 60-minute intervals are more commonly referred to as half-an-hour or hour, respectively). In the 45-minute case, the adjective 45-minute seems pretty common, for example:
a 45-minute class
a 45-minute lunch break
