I have a huge problem with photos on my wife's iPhone (5C, iOS 9.2.1). Even with the option to optimize them turned on, photos take more than 8.9 GB. Because phone runs out of disk space all the time. And what is worse, when I delete anything (Apps) after a while the free space is all eaten by the photos app again - it literally grows until the disk is full again. At the same time, all photos (and videos) stored at iCloud in their original quality take 14.6 GB of space. Those of you who have photos/disk optimalization on - could you check what relation between local and iCloud photos storage looks like in your case? I wonder if 8.9/14.6 is normal or not.