This issue has hit me many times lately, so I'm creating a post for easy reference. If you are starting from scratch with a Windows 7 SP1 ISO or CD, checking for updates through the Windows Update control panel can take hours. In my experience it will completely max out 1 core.
The easiest fix I've found is to install the April 2015 servicing stack update and then July 2016 update rollup.
Unfortunately the links above won't work on a brand new install because Microsoft is currently blocking IE 8. Use these direct links to download the updates:
April 2015 Servicing Stack Update:
The service stack update must be installed first or the update rollup will say it's not applicable to the computer!
July 2016 Update Rollup:
After rebooting, Windows should now check for updates in a reasonable amount of time. Hope this helps someone.