panoviewer
isn't strictly necessary; it replaces the JOSM core implementation for equirectangular images, which is CPU only. panoviewer
is hardware accelerated.
I'd bet it is a JOGL problem though; I think it would be fixed if the plugin moved to LWJGL. It might also be fixable by updating the version of JOGL used (it looks like JOGL has had some releases recently).
I haven't looked into panoviewer
in-depth, but it should be dependent upon the JOSM jogl plugin (written and maintained by kendzi; currently at v2.3.2 for JOGL).
For reference, JOGL had no real development for 7-8 years (v2.3.2 to v2.4.0). Updating JOGL will probably fix a lot of problems.