[Cura 2.6.2 and 2.7 runs EXTREMELY slow on PC]

Video drivers.

I had the same problem on my laptop. Windows kept 'updating' my video drivers to a version that just sucked for graphical updates. Slic3r, Sketchup, Cura, all slowed to a dead crawl.

I have Intel HD 4000 graphics chip and downloaded the two most recent driver updates from the Intel web site. Whenever M$ mucks with my Video Drivers, I just run either one (or both) to reload the good drivers and my PC screen updates go back to normal.

All of the other 3D applications on my system work fine. Sketchup, Altium, Solidworks, etc. are all very responsive. It's only Cura that I have issues with.

[Cura 2.6.2 and 2.7 runs EXTREMELY slow on PC]

That is really weird. Maybe another program is slowing Cura down? Like virusscanner or something?

I had the same thought. There is a virus scanner on the system that I do not have control over. I'm not sure how to determine if that's the cause without turning it off, but I don't have the permissions to do so.

[Cura 2.6.2 and 2.7 runs EXTREMELY slow on PC]

The results of running in the VM:

It works great. On the same machine that runs super slow natively (Windows 10), I can run a VM (Ubuntu 16.04) with Cura inside it, and it works great. Nothing I have tried gets it running at anything close to bearable native.

[Cura 2.6.2 and 2.7 runs EXTREMELY slow on PC]

I have a very similar issue on one PC. It has been so slow as to be unusable with any Cura v2 build. On other PCs it has been fine. I have tried uninstall / reinstall, deleting any settings I could find, etc. Today, I'm going to try within a VM running on that machine.