Adobe Installers do not migrated 3 party Photoshop Plug-in when a new major version of Photoshop is installed. To make maintenance easier for myself I install Photoshop Plug_in into a folder I create. When an Adobe update install the next major Photoshop version all I do is link the Photoshop Plug-in folder to my folder.. That way all Photoshop version use the plug-in files and I do not have to install plug-ins one at a time for new version of Photoshop and have to maintain multiple copies if plug-ins files.
You can un install versions of photoshop you no longer feel you need. Be sure you do not need any one you un install. Adobe does not make old version installers available to reloads version you remove. If Adobe introduces a new problem you will not have you old version available to get your work done. Compatibility issue exist between Photoshop versions. Adobe Add, Removes and Changes Photoshop features in Photoshop updates and new versions of Photoshop. All version of Photoshop have issues. You should always have more than one major version of Photoshop installed one yout machine.