Windows 7 update service is slow to begin with, but trying it on a computer that has been off for a while is damn near impossible. This is a known issue, apparently.
You need KB3172605 to fix it.
Then supposedly, to make Windows Update faster, you can install KB2852386 to be able to remove old updates with the cleanup wizard. But, the option to remove unneeded Windows Update files never appeared for me.
- Superuser – windows-7-sp1-windows-update-stuck-checking-for-updates
- Seven Forums – windows-updates-remove-outdated-updates-windows-7