While there can be a variety of reasons for a PC to perform project builds very slowly, we have found one very unlikely suspect that can have a dramatic impact on build times.
If you have a Logitech webcam, its driver may be consuming an inordinate amount of CPU time. Notice in this screenshot how the webcam driver LVPrcSrv is consuming 83% of the CPU's time:
This caused a simple build to take over 14 minutes. The solution is to end the process. After that, builds should proceed quickly as expected.
If you are not using the webcam, a more long term solution is to uninstall the webcam driver under the Windows Device Manager.
For more information, see Logitech's forums: