UNISOC platform devices aren't fully realme UI. It's a customized UI. The new features brought by major version upgrades are different.
What is new about Android 15 for UNISOC Platform Devices?
New features:
Adds Adaptive Battery, where you can view the apps that consume a lot of battery power.
Now you can quickly switch your audio output between the built-in speakers and external Bluetooth speakers.
Adds the Hearing devices shortcut to Quick Settings and additional features when hearing devices are connected.
Adds a Private space where you can hide or lock apps for privacy.