The problem is, the circuit further down the line does division calculations using this 15v rail.
This board belongs to a friend of mine, and is 12+ years old (the PCB, not him).
He wants to know why his readings are slightly off in his logging software.
I removed the 15v regulator and pumped in a clean 15v and his processor starting reading accurately again.
So, first off... poor design I would say.
I just replaced the regulator with one that is identical, but has a higher current ability. Just out of interest.
Same voltage.
So I just changed the 11.3k to an 11.5k and got 15.04v. So this looks like a winner.
I could cut the trace on the PCB so that I can test the regulator unloaded (there is no other way to achieve that test). But I don't want to mess up his PCB.
The math says 1k and 11.3k should equal an output of 15v, but hey ho.
I also replaced the 10nf capacitor that connects to the boost pin, as apparently that can influence the output, but that seems fine.