Zorin OS 16 will continue to receive support for a little longer, until April of next year, so you still have some time to make this upgrade.
There are always reasons to upgrade like more up-to-date packages and whatnot, but newer doesn't necessarily mean better. In my opinion, if something works, don't touch it.
If you wait, at least, you will have time to prepare things like what software do you need, make proper backup copies of personal data, etc.
One more thing, and again this is personal preference, but I would consider installing from scratch instead of going through the Upgrade tool. The reason is simple: this gives you a fresh start, without any files or software that you forgot to delete, traces of configuration files from software that you did delete, etc. It's also a good excuse to go through your files and decide what is important and what isn't anymore.