1. Design Changes: The iPhone 15 is expected to undergo a significant design change, similar to the transition from the iPhone 11 to the iPhone 12. This may include more compact dimensions, thinner bezels around the display, and potentially, a smaller notch or under-display Face ID technology.

2. Improved Cameras: Apple is always pushing for better camera quality in its smartphones, and the iPhone 15 is no exception. Rumors suggest that the next-gen iPhone series will have enhanced cameras with better low-light performance, higher resolution image sensors, and more advanced computational photography capabilities.

3. ProMotion Display: The iPhone 15 could finally see the introduction of ProMotion technology for its display. This means that the screen could offer a variable refresh rate up to 120Hz, providing smoother scrolling and more fluid animations.

4. More Powerful Processor: The next-generation A-series chip will further enhance the processing power of the iPhone 15. We can expect faster performance and increased energy efficiency with every new-generation chip from Apple.

5. New Biometric Features: Some rumors suggest that Apple might include a new biometric authentication method in addition to Face ID, such as an under-display Touch ID fingerprint sensor or improved facial recognition technology for faster and more secure unlocking of the device.

6. Better Battery Life: With every new iteration of the iPhone, battery life usually sees some improvement. Considering consumer demands for extended battery life between charges, we can expect that Apple will deliver on this front with new battery technologies or more efficient components in the iPhone 15.

7. Expanded Storage Options: While we don’t have exact details yet, it is likely that Apple will continue to offer higher storage capacities with its upcoming iPhones, perhaps starting at 128 GB and going up to 1 TB or more for its top-tier models.

8. Enhanced Durability: The iPhone 15 may come with even better durability and water resistance than its predecessors, making it more robust and less prone to accidental damage.

9. 5G Connectivity Improvements: As 5G technology continues to mature, we can expect the iPhone 15 to support even faster download and upload speeds, along with expanded coverage for improved connectivity.

10. Portless Design: Some reports suggest that Apple might eventually move towards a completely portless design in the future. While this may not happen with the iPhone 15, it’s something worth keeping an eye on as wireless technology becomes more prevalent.

11. Release Date: Though the exact release date remains unknown, based on historical patterns, we can expect Apple to launch the iPhone 15 sometime in September or October of its release year.

Keep in mind that these are all based on rumors and leaks; nothing is confirmed until Apple officially unveils the iPhone 15 at a future event. However, these are some of the most prominent features and improvements expected in Apple’s next-gen smartphone series.