Thanks @bogovicj for summarizing the situation.
Unfortunately, there is one additional point: for macOS Sierra and High Sierra, there are often fatal problems with Java 6 + Java 3D 1.5 now. It seems that the OS upgrades from earlier versions remove critical pieces of the Java framework, which do not get installed into the same places when you download and install Java 6 manually on Sierra or High Sierra systems. See this thread for details.
So if your goal is to “stick with Java 6 + Java 3D 1.5” then I would also suggest not upgrading to Sierra or High Sierra. The situation is problematic enough now that I may need to pour in more development resources (myself or one of my students) early next year to make Java 8 + Java 3D 1.6 work better on the latest macOS versions.
@Oshawott Have you tried using SciView? It is still alpha quality, but built on newer technology which may work better for you.