Even then, I think 15 years of support for a Linux distribution is a bad idea anyway - software just moves way faster than that. How supported is that release really going to be after 14 years, even with the best of effort?
Is every upstream package going to be version compatible with a 15 year old release with no breaking changes? And if it's not, and you patch around that or freeze those packages, is your software still "supported"? What if there are unpatched critical issues? Is that a better idea than keeping up-to-date with a rolling 24/36/48 month release cycle?
In the analogy of a roof or a basic appliance that's fine, but the long-term support equivalent of that is have a copy of the software on a couple of USB drives and disconnect the machine from the internet completely. As long as you don't do anything novel with it, it'll probably work for decades. There are still Windows 3.1 terminals in the wild somewhere.