FYI- much lower. At 15,000’ you need oxygen (or pressurized cabin), which most small planes do not have. I don’t think you’d need a supercharger yet, but many engines would be struggling

I was a passenger on a small plane where they only had oxygen for the pilots. I believe it was at 15,000 ‘. It was surreal: it didn’t take long for the blackness to start closing in from the sides until I could only see a small tunnel in front of me. I don’t know if I should have been worried for my life but I clearly would not have been capable of flying.

A standard air breathing small Plane without supercharger or other altitude adaptation, can take a long time and a lot of fuel to get up to 15,000’ as the engine gets weaker with thinner air. It’s generally not worth trying to go this high unless you’re in a longer trip (the article doesn’t say anything about the plane though so if it had a supercharger and oxygen, then disregard this. Nothing I say applies to anything with a turbine)

One of the most common training aircraft is a Cessna 152. Google tells me it has a ceiling of 14,700’. It can’t even reach 15,000’ (depending on air pressure)