No stupid questions when dealing with 4500 PSI. High pressure air can injure or kill.
Here's a video that shows what a "Failing" tank can do. Granted, this tank failed due to gunshot wound.
https://www.youtube.com/watch?v=3_El-4k7xds
Regardless, when a tank fails, I'd rather be somewhere else.
As for the 15 year lifespan, that's Department of Transportation if I recall. All sorts of regulations around the HPA tanks. 15 years is the legal life span, not necessarily the actual life span. Key is that once it's older than 15, there's only one way to extend the life span with a new kind of Hydro Testing that the US Navy spearheaded. PA sells the extended life tanks,
https://www.pyramydair.com/s/a/Air_Venturi_Life_Extended_Carbon_Fiber_Tanks_4500_PSI/8677 With current costs, it seems an expensive way to extend the legal life of a tank.
Anyway, tanks under the kind of pressure we use for airguns, the expansion and contraction of the tanks over time may cause cracks, and cause an eventual failure. No guarantee either way, so it's kind of a crap shoot.
Good luck on the hunt for tanks, it's always an adventure