When to upgrade iphone 15 pro

I've had mine since it came out and the biggest reason to buy a new one is storage, I got the 128 and I keep getting notifications that my storage is full. Which is weird because it's mainly WhatsApp and photos, and they're about 25GB combined. Still, I would like the 256 next time.

Biggest thing for me is the camera, so how big is the difference between my current camera and the 16 of 17 pro?