Have you guys tried saving after the long load, then loading that save?
Initial 10+ minute loading times after an update is to be expected on saves from before the update. This happens when the story is rebuilding to incorporate the new changes. The same thing will happen when a mod with story scripts updates, and your save's story needs to rebuild to integrate the changes.
After that long load, saves made after that should load at a normal speed, since it doesn't need to rebuild after that point.
Obviously this won't apply to everybody, as the long load could be due to other issues, but this is a common cause of it.
