I have 14gb of photos and videos that I transfered to iCloud photo library using this method.
1. Download an app called rollit, photo transfer app on your iphone/ipad
2. Connect device to computer and open iTunes
3. Navigate to where you manage your apps in iTunes
4. Find rollit at the bottom in the section where you can manage files through apps
5. Drag all pictures and videos, no folders and let it sync and transfer
6. Once done open rollit app and you'll see all your pictures
7. Select all and transfer to camera roll, it might take a while. Pictures that have been transfered will disappear from rollit and appear in photos app. When I did it all pictures didn't transfer on the first go. I had to select all (the remaining pictures) and transfer again.
Everything will automatically transfer to iCloud photo library if it's already enabled.
As many others my camera roll is in wrong order. But all pictures I've taken after this method is correct. All pictures in moments are in the correct order and I can search for pictures using location etc. All info is saved. Only camera roll is wrong since rollit probably does a random transfer and not it the order the pictures are in the folder.
Hope this helps