It introduced several new features, enhancements, and performance improvements. Some of the notable features included in JDK 15 were:

1. Sealed Classes: The sealed classes feature allowed developers to control which other classes or interfaces can extend or implement them, providing better control over class hierarchies.
2. Hidden Classes: This feature provided a mechanism to create classes that are not discoverable by reflection, enhancing security and reducing the risk of potential abuse.
3. Z Garbage Collector (ZGC) Improvements: JDK 15 included various enhancements to the Z Garbage Collector, aiming to improve the overall garbage collection performance and reduce latency.
4. Pattern Matching for instanceof: The instanceof operator was improved to support pattern matching, making it easier to work with the contents of objects after checking their type.
5. Records (Preview): JDK 15 continued the preview of the records feature introduced in JDK 14. Records are a concise way to declare classes that mainly act as data carriers, automatically generating useful methods like equals(), hashCode(), and toString().
6. : JDK 15 improved text blocks, which were introduced as a preview feature in JDK Text Blocks13. Text blocks make it easier to define multiline strings in Java code, enhancing code readability.

Please note that newer JDK versions might have been released since my last update. To get the most up-to-date information on JDK versions and features, I recommend checking the official Oracle or OpenJDK websites or other reputable sources.