Thanks Mark, I'll try that. I'm running a NVIDIA GeForce GT720 2GB.
UPDATE: windows 10 appears to have removed the hardware acceleration option from all of the menu items in the control panel, and I'm not happy about doing it via the registry. I uninstalled 1.9 and then reinstalled it, thinking that perhaps the LUTS (there were quite a few) that I had imported was causing AP to slow right down, or perhaps the Nik collection that I had added as a plug in. However, even on the reinstall it is outstandingly slow. Sliders still won't work without significant lag, clicking on the LUTS tab in the adjustment column results in a minutes long freeze.
So.....1.9 is not working for me. I'm back to version 1.8.5. Disappointed, as this is the first time I've had any issue with AP along these lines.