There are no existing plans to support Java 15. That’s not to say that if changes can be made to facilitate support we’re unwilling to accommodate, but I currently do not expect us to actively pursue them.
Given the high frequency with with Java releases occur, it is good to assume that generally, only LTS versions of Java will (eventually) be supported.
If you’re in need of support for specific versions of Java, and are unwilling or unable to implement that support yourself, you could consider enlisting help from one of the commercial support providers, who might be willing to help you.