iPhone 11 syncing, but iPhone 6s Plus not updating iCloud Photos/Voice Memos (iCloud Storage full)

Hello everyone! I'm new to the Support Community.

I've recently gotten my hands on an iPhone 11 (iOS 16.2), and I've transferred my data from my old iPhone 6s Plus (iOS 15.8) onto it.

After clearing some backups and documents to free up space, my new photos on the iPhone 11 are syncing correctly with iCloud, as confirmed on icloud.com. However, my iPhone 6s Plus is having trouble reflecting these changes. Deleted and newly added files (including images and voice memos) are not updating on it. Previously local images that have been uploaded do not have the synced tick.

At the bottom of the Library tab, "Restore from iCloud paused" is shown on my iPhone 11, and "Updating..." on my iPhone 6s Plus along with an iCloud Storage warning on both devices.

WLAN connection is stable and fine. Crucially, my iCloud storage is currently full, 5/5GB, and almost full on my 6s Plus, 15.4/16GB.

I've tried the following on my 6s Plus:

• Restarting the device
• Turning iCloud Photos off and on
• Signing out and back into my Apple ID

So my main question is: Is the full iCloud storage likely the reason why my iPhone 6s Plus isn't updating with the changes? Are there any other potential causes or troubleshooting steps I should consider given the full storage situation?

Thank you for any help!