I think there might still be a few issues open on the 0.15.0 milestone related to the release notes. achow101 will be able to give us a definitive answer, if he's not too busy.
I did find out a post by Peter Wiulle explaining the situation:
It's not released, just tagged. OP was a bit too soon, see the first comment
Tagging means that the source code is finalized, but there are still a few steps remaining before the release (such as building binaries, verifying that all developers agree on the result, finalizing release notes, publishing in various locations, ...). This will happen in the next few days. Only after that will distributions have the ability to pick it up.
/u/nullc was pointing out that building from source is much easier on Linux based systems. He wasn't talking about it being prepackaged in distribution repositories already.
So it looks like we will need to wait for a couple of days?
https://www.reddit.com/r/Bitcoin/comments/6zhxf2/bitcoin_core_v0150_final_is_out/dmvu5v1/?context=3