I am currently at 15.04. I want to upgrade to a stable version soon, but after I finish some projects I am working on every day. I assume these projects will take another 6-8 weeks, but my system is now complaining about system errors and that there are no software updates for this version.
I can still use my computer, but how long will it will take before this all comes crashing down? Do I have enough time to finish my projects, or should I update immediately?
Never.
Smart to keep running an unsupported operating system? Well that totally depends on the use case.
Security wise of course it is not a good idea since updates will cease so using an unsupported operating system will increase holes in software that could be abused.
Now let's assume you have no internet on a system. Not directly and not indirectly. If that is the case even using 4.06 is possible.
By the way: your way of working needs evaluating ;)
If I was you I would have started those projects in such a way that an update would not mess with it. For instance: install all software you needed for our in /opt so you could copy/paste it into a new version of your operating system, or use virtual box or, VMware to install on operating system and work from there. There are several ways to keep your software working and being able to keep your system up to date.
