Why is KNLMeansCL slowing me down so much

[Selur]

Since I don't know the history when it stopped to work my guess is that some update killed the old drivers which worked (and may be where at least partially from before you upgraded to Windows 10, guessing that you didn't to a clean new install) and installed newer once.
About the intel cpu, from what I read is that sometimes when an AMD card is detected the OpenCL support of the intel cpu is ignored,...
I'm by no means an expert on this nor do I own any Hardware that is as old as yours, so I can only speculate from what I read through searching for this,..

Cu Selur