As an experiment, turn off the GPU acceleration in Lightroom and see if this improves. (Go to Preferences, click on the Performance tab, then uncheck the box).
Also, please let us know if you are doing a lot of brusing and/or a lot of spot healing on your photos.
Also, please state the EXACT make and model of your CPU.
As noted above, I've already tried turning off GPU acceleration a number of times per other questions on this site and so far I've seen no measurable change in performance. I am occasionally doing some spot healing (10-15 per photo max for things like sensor dust in skies of random tree branches on the edge of a frame) and definitely doing some brushing. However, the performance problems for just general rending of an image is happening even on photos that have not been touched in any way in the Develop module.
A little hard to find the 'exact' processor data since Apple doesn't expose the model number easily but from that I can find it's a Haswell, Quad Core 4.0GHz Core i7, Intel 4790K processor
As an experiment, please create a new catalog, put a dozen or so photos in there (not important photos, though) and then edit the photos but DO NOT do any spot healing or brushing on the photos. Is the performance acceptable? Then continue to edit the photos with the usual amount of spot healing and brushing. Is the performance worse?
Turning off turning off GPU makes it slower for me