Well, I believe some people needs to pay attention to this post right here! I can confirm it.
Last night my XB1 was on instant mode the entire night, and it did not updated (I think), then I turned the console off with energy saving mode and turned it on again, the update wasnt there yet. However... I've left my XB1 on instant on yesterday the entire day, this morning when I woke up I checked: still 45GB. Then I turned it off again in energy saving mode and went to university. Just arrived home from university, turned on my console again (from cold boot) and it is 59.1GB now.
So there's a bug on the system I guess. Maybe for preview members?
I almost deleted the whole game and installed it again! Thanks for that tip man, I would not check its size again this afternoon if it wasnt you.
In your case there must be something wrong. Or this is still installing. Because there should be 59.1GB, and not 57.9.