Lag during editing

I have been experiencing a slow down of sorts when editing in C1. Every time I make any adjustment to and image(levels, color balance, contract etc.), the image preview lags a bit. When toggling back and forth(undo - redo) to see the difference in an adjustment, the image preview lags and it's super hard to see small changes in adjustment because of this. I'm not sure what has happened as things had been running fine up until just recently.

I currently have a catalog of around 9,000 images, using an imac running 10.11.1

Any suggestions would be greatly appreciated..