I have encountered this same bug moving around 1,000 image files between local folders with Ubuntu 15.10. Killing the process, disabling preview (as suggested by khadgaray in comment #7) then trying again made the move nearly instantaneous. Re-enabling preview after the move showed the correct file previews in the new folder immediately. Therefore the problem (for me at least) seems to be entirely in the image preview process).
Package nautilus:
i 1:3.14.2-0ubuntu9.1 vivid-updates
I have encountered this same bug moving around 1,000 image files between local folders with Ubuntu 15.10. Killing the process, disabling preview (as suggested by khadgaray in comment #7) then trying again made the move nearly instantaneous. Re-enabling preview after the move showed the correct file previews in the new folder immediately. Therefore the problem (for me at least) seems to be entirely in the image preview process).
Package nautilus:
i 1:3.14.2-0ubuntu9.1 vivid-updates