You’re using the term “performance issue” but the only thing you actually complain about is the memory usage. Your Zammad version is over 12 months old and has security advisories.
Patching in general helps to get rid of bugs, keeping it up to date etc etc.
If that’s not enough arguments for you, then I guess, no, you don’t have to update.
Zammad is not a set and forget piece of software.