The only ones I've come across have been in thermal tracking for bias stabilisation in audio output stages. They are, AFAIK, made of multiple stacked silicon junctions up to the specified forward voltage and are used forward biased to track the output devices.
The ones I've seen were rated at a Vf of around 4V and I used a chain of SMD rectifier diodes to obtain the right reference for the job. 15V obtained this way might be a bit ambitious!
