It is quite usual that LR takes time to build previews, i would suggest you to build 1:1 previews and run it all night.
This is quite abnormal. I have not noticed much difference in import speed between LR 5 and CC 2015. Certainly not a factor of over 10 like you are reporting here. This has nothing to do with preview building time so ignore the other answer. There is no good reason to build 1:1 previews for most people's workflow. This also has nothing to do with display calibration. Somehow Lightroom is not reading the files' built-in preview. This looks a lot like you have a problem with the connection to the camera as this is absolutely not normal. It should populate the image previews in import fairly quickly. Not as quick as Photos but fairly close. Have you tried a card reader instead of connecting directly to the camera? Card readers are generally many times faster than connecting over USB. Your iMac has a built-in SD reader that you could try if your camera is the mk II version that can use SD cards, otherwise card readers cost $10 and are more reliable and faster than connecting using USB cable. Another thing to try is to import using the operating system to a folder on your hard disk and then import from there.
I've tested the cable, card, and camera on other machines. Consistently, any photo program such as photos, picas, or even the old iPhotos all recognize the previews directly off of the camera. I wonder if there is a specific driver my Lightroom CC is somehow lacking for the Canon 7D. Is it because my 7D camera is several years old? I think you're right I may have to use a program other than lightroom to import my photos. I'm just disappointed to not use Lightroom to import as it's ability to handle many raw photos was its key useful feature.
The suggestions were mostly for troubleshooting testing. Lightroom should show you the previews for this camera no problem. You should even be able to shoot tethered this way. So the fact that it doesn't work right indicates a problem to me. I just wanted to get hardware out of the way to see whether Lightroom was the issue. The recommendation for a card reader was more general as it is almost always a lot faster even if the direct camera connection works fine.