You start your question by saying you have limited storage so I have taken the liberty of proposing a solution that doesn't delete, but instead stores smaller versions of your photos.
Look at this Apple doc iCloud Photo Library FAQ, if the goal is simply to save space there are approaches that will help you in the
Quoting rather liberally from that article just in case Apple changes it when iOS 10 comes out:
Can I use iCloud Photo Library to save space on my device?
iCloud Photo Library automatically keeps all your photos and videos in
the original, high-resolution version. Follow these steps to choose
how you store your photos and videos on your device:
On your iPhone, iPad, or iPod touch, tap Settings > iCloud > Photos or
Settings > Photos & Camera, then select a storage setting. On your
Mac, click Photos > Preferences > iCloud, then select a storage
If you turn on Optimize [device] Storage, iCloud Photo Library will
automatically manage the size of your library on your device, so you
can make the most of your device's storage and access more photos than
ever. All of your original, full-resolution photos and videos are
stored in iCloud while device-size versions are kept on your device.
You can download the original photos and videos over Wi-Fi or cellular
when you need them.
I worked the phones for Applecare during the iOS 6, 7 and 8 releases. We were mushrooms, we were kept in the dark until a day or two before the release, then all this new training would hit. I am not sure who is more frustrated by Apple's constant changes in Photo Stream / iCloud Drive / iCloud Photo library, the employees or the customers! I hope Apple can settle into something their users can understand for the long term. Hope this helps.