Dave
I really appreciate the time you are taking to help me on this.
I am using Win 7 Home Premium. I do not recall having any issue installing SU-8 when I had my XP HD crash, then upgraded my
drive to an SSD and loaded Win 7. I reinstalled everything on it from scratch, using my old recovered HD as only a data repository. For SU-8 after a reinstall on the SSD, I mainly just copied the contents of directories to get back up. I know I cannot do this with SU-15. Well, my fav template got copied over no problem. 
I do remember still having a bitch of a time configuring my SU-8 to what I was used too.
There really should be a tool to automate upgrade conversions, especially if SU is now on an annual update path. I have never encountered an app that needed this much work to effect an upgrade, or even a reinstall.
Anyway, this time, in anticipation, I wrote down on paper every aspect of SU-8, file locations, toolbars, preferences, etc. Some were screen shots, others were printouts, ie: shortcuts. I exxed off the rarely used and never used plugins, but still had a lot of needs and used often plugins to load. I am about 1/2 way there.
It wasn't 2 full days, but to date about 10+ hours and counting trying to get SU-15 to feel like my old SU-8. There are plugins that have changed names, there are plugins and tools that I always thought were native SU, there are plugin names that bear no resemblance to the menus and tools they provide, there are RBZ plugins in Sketchucation, and more not in the store that I need or use often. And to top it all off there are new native tools that used to be plugins, and all of the tool icons look different, as well as menu location changes. Plus there are toolbars I had in SU-8 I cannot find in SU-13; perhaps they are a custom TB. Confusing for my 70 year old head.
I'll admit I am not one to play with SU and understand its inner workings...
To me SU is a tool to draw stuff, and even then I use maybe 50% of its capabilities.
Yet on average, I spend about 6 to 10 hours a day in SU. It is hands down my most used app on my PC. But most of the configuration setup on SU-8 was done years ago in SU-3, 5 and 7 so a lot of stuff I have forgotten how to do. Hence my opening line in this thread.
Right now, I have pretty well loaded the store of what I need and use into the extensions library. Two of them I just loaded, Pipe along path and CofG were the first I tested. I drew a wavy line and PaP'd it. Noted extra parameters to explore later, but that went well.
Then I tried CoG and SU-15 froze.
I had to crash it. No bugsplat.
Then I came here.
Next thing is to tryout all the extensions, then search for the list of RB's I need and install them.
TTFN