After working from scratch I find the issue lies in the GREP styles. Without any GREP styles, spell check finishes in a flash. With a GREP style to control runts with nobreak, such as .{6}$ , it slows spell check somewhat, but not excessively. However, I recently added two GREP queries that use a lookbehind, and hence, parentheses, and when these are in use things get much worse.
I found the following information useful in figuring this out: https://creativepro.com/speed-grep-styles/.
Since I need those lookbehind GREP styles to maintain capitalization in the underlying text, as I mimick Small Caps, I've decided to create an alternate "based-on" style that does not use any GREP styles during the spell check.
My methods may not be what others would employ, but until the spell checking, I had seen no significant degradation in performance. Even now I have 2 different documents open using similar GREP styles, including one that was held up here as a questionable example, yet the document with that bad GREP style runs spell check much faster than the one that has GREP with lookbehinds in use.
I had a bad attitude when I opened this discussion. I apologize.