May I know the version of Lightroom and Photoshop?
If you are using the latest version of Lightroom ,then please update it to 6.3/ 2015.3?
It's your Mac and OS X along with whatever else you have running that is hogging the system resources.
No, it is not system resources being hogged and I am on the very latest versions of both LR (2105.3) and PS (2015.1.1).
When opening from a fresh boot of the system with only LR running it took 39 seconds from the time I clicked Edit In Photoshop for the "Edit w/ LR Adjustments / Edit Copy / Edit Original" box to appear. After selecting the option, PS then proceeds to open and that speed is fine. There is also a noticeable slow down in the response of the edit tools - when LR is the only program open. CPU usage is commonly under 5% and available memory is in the 15 - 18 GB range so it is not running out of system capacity.
Once I get to the "Edit w/ LR Adjustments / Edit Copy / Edit Original" box, if I click Cancel I get a "Saving Metadata" progress slider in the top left and when it gets a third of the way done it pop up a window that says "One or more of these photos has been changed in an external application. Should Lightroom overwrite the settings on disk?" If you hit cancel it starts to save the metadata again and then pops up the same window again. The only way out of it is to answer Overwrite and then it will show as many progress bars as the number of times you hit cancel. Then it is likely to freeze and produce an Error window that says "Some save metadata operations were not performed." The error listed is Unknown file I/O error. (4) What is particularly troubling is the multiple files are listed as problematic but I was only trying to move one to Photoshop and no others were in any way touched while I was in LR.
Something is very wrong here and I need any help I can get. Kind of a pisser to have a fast computer with lots of RAM and have LR act like a drunk pig in slow motion.