Battery health issues on iPhone 15 Pro

Batteries, like people are individuals. No two people age exactly the same and batteries don’t age the same either. The exact usage, chemical makeup, storage conditions, exposure to heat and cold and about a dozen other factors mean that every battery ages differently. Battery aging is not a linear (straight line) and degrades at different rates as the chemicals in the battery age and other factors mentioned above. The graph below shows the 4 batteries that were recharged differently and look how differently the batteries capacity changed with age. There is nothing linear in the aging process.

Apple expects your battery health to be at 80% after 24 months. If your battery health misses that expectation, contact Apple Support.

Please review the Apple Support articles on battery optimization. It contains the best  current practices for battery charging.

About Charge Limit and Optimized Battery Charging on iPhone - Apple Support

iPhone Battery and Performance - Apple Support

Batteries - Maximizing Performance - Apple

About the battery and performance of iPhone 11 and later - Apple Support

My opinion......Battery Health should be about 95%. Take the phone in to an Apple Store or an authorized Apple service shop to have the battery checked and tested.

Unfortunately, you will likely be told that there is nothing wrong with your battery.....and that might be true. Sometimes, you just run into bad luck.