I think we're into the "Is a supercar really worth 10x a Mondeo" territory.
I guess there are many factors and I don't know the skill, expertise, product demand, man-hours required, and so-on involved.
How many instruments do they make a year? If it's 10, then £15k is not going to furnish a lavish lifestyle, whereas if it's 1000 then they're probably doing very nicely!