I have a small office (<10 phones) with a rock-solid FreePBX 15/Telnyx/Vultr system that’s been running for 2 years. We use only basic features and really have no complaints with the system.
My usual attitude is “If it ain’t broke, don’t fix it”. That said, is there any compelling reason to upgrade from 15 to 16? If I do, am I best to upgrade in place, or try restoring settings to a new installation from the ISO?