To take advantage of the new push notification features in iOS 15, mobile marketers will need to update their apps to use the new API. The new API provides more flexibility and control over notifications, allowing for more targeted and personalized messages to be sent to users.

To update to the new API, developers will need to make changes to their app's code. The specifics of these changes will depend on the app's current implementation and the desired notification functionality. Apple provides detailed documentation on the new API, including sample code and guides for migration.