We know that 1507 will be officially out of support next year but 1511 is the highest OS that this software can run. For some of the computers, we have to update it to 1511 just to get the RX 6000 GPUs to work properly. It may be a security risk but we could not find other solution other than installing an older GPU that supports it.
So you have had 12+ months to invest/research and decide on a fully supported solution and you want to still kick the can down the road again and again?
What you should have been doing is segregating the older machines off to the current CNC hardware and stockpiling some spares for the longer term support you are inevitably going to have, while investing in newer machines and software for the newer CNC machines you are getting ahold of. You are going to very quickly run into an issue where hardware failures of you current hardware wont have replacement parts and suddenly your scrambling to try and find retrofits or playing eBay roulette for 15 year old hardware. Where as you could have "retired" a few of the current machines and stored them away for that scenario in a few years time.
Trying to get a machine to do this all in one going forward is going to be both extremely hard and problematic to support in the longer term when the other older parts inevitably fail. (Motherboards, RAM, interface cards etc)