I don't know the answer to your problem, but maybe you can give some more info:
1. How many files/directories are you working on? I use the R.Slideshow a lot in one specific directory structure containing 1000 files spread over 11 directories. Very fast. Maybe your numbers far far exceed this? I will try it later on a higher level containing 12000 files in 250 directories. Will report the reaction time.
2. What version and SVN of MP are you using?
3. Maybe you can include your logfiles. Easy to generate and share by using the MPTestTool2.exe in your MP directory.