Well, that was a totally different experience. I downloaded the file, and it opened in RT pretty quickly. I applied the Neutral profile and saved the image. The processing took a couple of seconds, and there was no abnormal disk usage.
With the file I had problems with, I followed the ‘basic’ editing steps outlined in the RT introduction - adjusting WB, colour, sharpness and cropping. I suspect that file might have been bigger than the 10MB you shared, or my changes were too big for my 4GB RAM to deal with without resorting to the swap file (as heckflosse suggests). If its the latter, I guess that means more RAM is in order.
Does anyone know if 4GB RAM is now considered insufficient for basic editing in RT?
Thanks for your help.