It's 30%. It's only 15% after 12 months of a customer rebilling which is statistically insignificant number, and it was only done as a carefully orchestrated PR move to make people think 15% when it's really 30 - as you have demonstrated
A typical customer lifetime might be somewhere between a year and two years, unless you happen to be a giant like Netflix.
Let’s say you expect your customer to churn after 14 months, so that means you only enjoy 2 months of Apple’s reduced royalty rate. Your total average rate is 27%.
This concept is why many sunscription services are able to offer lifetime subscriptions. They have already figured out what one customer is worth based on churn rate, so the lifetime subscription is set up to be a price that matches or exceeds that number.
(Not that meal kit companies would be paying Apple 30%)