I use an out of date tank, I only fill it to 4200 psi, most times less. It's been two years and probably 30-40 refills no issues I keep a close eye on it. I understand the risks associated with it, but I also understand there are risk associated with any high pressure system. New equipment fails also. I wear a face shield and hearing protection when refilling.
The 15 year service life is a one-size-fits-all rule that doesn't reflect the lifespan of the tank. As people have said, you can get tank re-certified for another 15 years. However, some people are binary thinkers, black and white. They believe a tank on the last day of its life is safe and the next day it is dangerous. Does that make any sense to you? I would also not put too much faith in the word of people trying to sell you second hand tanks, just like anyone trying to sell you something. Certain tank sellers are particularly douchy, I will say. Do your own research and make up your own mind.
If you decide to go with a second hand tank, find one that is already full and holding air [even if they drain it for shipping] and find a picture of the actual tank you are buying, not a sample from a lot of 25-50, etc. Good luck!!