PostgreSQL 15 introduces several improvements, including enhanced sort performance and write-ahead log file compression. The SQL MERGE query can now update, insert, or delete rows with a single statement, handling concurrent insertions differently than the INSERT ON CONFLICT statement. PostgreSQL 15 also removes the global write privilege from the public schema to limit potential security issues, allowing users to grant specific permissions to trusted individuals. Additionally, the database treats NULL values as not distinct in unique constraints and indexes, preventing duplicate key value violations. Users can try out these features by creating a PostgresSQL 15 project with Neon's SQL Editor at https://neon.tech.