In some environments, SIM upgrade is taking a very long time (mostly over several hours).
Release: 8.6, 8.7
While this can be valid for a slow machine, it has been found that pending reboot requirement causes Windows MSInstaller to work very slowly.
Try rebooting the machine prior to the upgrade. It resolves in most cases the issue.
When SIM is launched it may show up a message that reboot is required.