A point release is not a separate, new version of Whonix ™. Instead, it is a re-release of Whonix ™ which is inclusive of all updates up to a certain point.
Installing any version of Whonix ™ 15 and fully updating it leads to a system which is (mostly) identical to installing a Whonix ™ point release.
If the Whonix ™ installation is updated, no further action is required.
Regardless of the current installed version of Whonix ™, if users wish to install (or reinstall) Whonix ™ for any reason, then the point release is a convenient and more secure method, since it bundles all Whonix ™ updates that are available at that specific time. 
What is better? Upgrade or Image Re-Installation? See Upgrade vs Image Re-Installation.
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