That’s a stay of execution at best. At some point, you’ll need to upgrade to a new Unity. It might be because IOS and Android require using an SDK that’s not more than 2 years out of date, or because nVidia/AMD invented some new amazing tech, or a host of other reasons. But eventually, you’ll need to upgrade.

The worst part is that Android is actually removing apps that haven’t updated in years, even if they still work perfectly. So you’ll get screwed by that eventually if you do mobile at all.