Thanks for your reply, Nikolay.
Here is the issue that caused me to suspect the TS extension was causing my issue:
I use autohotkey (AHK - https://autohotkey.com). After installing TS, my AHK macros were extremely slowly -- I could possibly type faster. Naturally, I assumed it was something else slowing
my system down, but I couldn't find anything obvious in Task
Manager -- nothing was showing more than 2 or 3% CPU. Reading AHK's Help to refresh my memory as to performance issues I did stumble
on (not an exact quote) "maybe something else has installed
keyboard hooks that are slowing your AHK scripts down".
might expect, that was the a-ha! moment. I killed visual studio (which also killed the TS extension inside
it) and also killed the TS app. AHK macros went back to normal performance. Hmm. I started the TS
app, macros were only *slightly* slower.
Feeling I was now onto the culprit -- the TS extension in VS -- I tried removing it. That's what my original post is talking about. Ended up having to uninstall the whole of TS.
Having done that, and seen that AHK was performing normally, I reinstalled TS *without* the VS extension, ran TS and then tested AHK again. I was back to nice, speedy AHK macros.
Take-away: The Test Studio extension for Visual Studio messes with the responsiveness of system wide keyboard hooks used by other software.
Thanks for reading,