When you’re making this statement you need to be a little more specific on the users. You mean the end users of your PBX deployment? Because then I’ll bite on the 99% of users claim. However, when talking about FreePBX and the Adming GUI the only users would be those with administrative access. I’m not biting on 99% of them being non-technical.
Additionally, while your statement is mainly true (most don’t care what version as long as it works) there is also a follow up to that statement. They don’t care until things start to break when they actually try to do something more. Then they care a great deal to the point they get overly defensive about never updating for almost a decade when asking for help.
Now as I have pointed out before there was an issue with GPG a few years back, bigger than just FreePBX.
This one is from 2016
GPG Verify File check failed - FreePBX - FreePBX Community Forums
This one is from 2019
What is the GPG issue? - FreePBX / Security - FreePBX Community Forums
There are quite a few threads from 2019 and older about the issues with GPG and older keys being poisoned. All of this was handle at the time it was an actual issue and resolutions where current for it. Now that more time has based and there have been various updates to OSes and other levels of software on those systems. The solutions that worked 3-4 years ago might not work now.
The easiest and the most efficient solution to this is to backup your current PBX, install v15 and then restore your backup to it. I have yet to see an actual valid reason as to why this is not the approach being taken thus far.