I downloaded the macOS Sierra (GM) and installed it on my MacBook. Before I installed it a backed up all my data that isn't stored in the cloud or somewhere else.
I'm using iCloud Photos to sync all my photos and videos with iCloud. Every photo and video is already in iCloud so I may don't need to back up my Photos library, but I did - just in case something goes wrong.
So I wiped off all the data from my MacBook to do a complete and clean installation of Sierra. Finally everything works fine and I'm going to get all my photos and videos back to the Photos app.
My backup of my photos and videos has ~13GB and I really have a slow internet connection, so it would be nice if I could use the backed up library instead of downloading everything from iCloud.
As soon as I open my library with Photos it starts importing and optimizing etc. and all photos and videos are there. But it starts uploading every single photo and video to iCloud? How can I tell Photos that my photos and videos are already in iCloud and it should stop uploading?