While 3CX does not officially support a version 16 install on a Windows 7 operating system, it DOES work! The upgrade from v15.5 SP6 to v16 went flawlessly with no issues.
However, doing so produces an un-supportable environment as Windows 7 will not be receiving security updates or feature updates in the new year, leaving the security of your entire platform on that machine at risk of zero day exploitation as flaws are discovered. Just because something works, does not mean its a good, reliable, or supportable idea. We just actually replaced our last windows 7 based 3cx server last night, with a linux build.
I strongly recommend you either bring the system up to a newer OS, or re-install it to linux.
I also hope that the 3CX Team will send out a notice to everyone warning them of this situation, and to get ahead of it before the cutoff which is now looming.