GTA 5 Title Update 1.15 includes the Independence Day Special content detailed here, but also brings additional "game tuning updates and other adjustments," Rockstar has announced.
The major addition is the new On Call Matchmaking, which allows players to access a Job invite and continue to play in Freemode until the Job is full. This means you should end up spending less time twiddling your thumbs waiting for a Job to begin.
A number of exploits have also been removed, including the ability to spawn UFOs in public sessions, the ability to duplicate vehicles, free Barber services, disappearing from the radar and more.
You'll find the complete patch notes over on the Rockstar support pages.
Source: Rockstar Support