How do I download photos from IPL onto my new iPhone?

I'm not entirely sure why this isn't working more seamlessly. I had a backup stored on iCloud and all of my photos & videos (19.8 gb worth) synced through iCloud Photo Library (optimization turned on, so it stored about 14-15gb?) on my iPhone 6. Just received my 6s yesterday and backup restored perfectly and beautifully, but my media is in a very confused state. I had assumed that once I set everything up, all the photos and videos from IPL would automatically download onto my phone. This time I have optimization turned off since I went up to 128 gb on my phone.

While the photos are all showing in my camera roll, they're not downloaded locally from what I can tell. Photos and videos take up only 6gb so far. If I open a video, I will get the little loading sign while it (I assume) downloads and plays. Longer videos of course take longer to download. How do I get my new iPhone to completely download everything that is on IPL?

I can't have it keep downloading mainly because 1) I feel like this takes up a lot of bandwidth 2) I'm a dancer, most of the videos I have are 4-10 minutes long and I constantly go back and review them while I'm training. The studio is located in a dead zone for most cell phone networks so having to download these videos from iCloud just takes way too much time.

thanks for any help!