[3.15] gh-133879: Announce final release in What's New in Python 3.15 (GH-158256) (#159053)

Co-authored-by: Hugo van Kemenade <1324225+hugovk@users.noreply.github.com>

Author: miss-islington

Doc/whatsnew/3.14.rst

@@ -60,7 +60,7 @@ Summary -- Release highlights
 .. This section singles out the most important changes in Python 3.14.
    Brevity is key.
 
-Python 3.14 is the latest stable release of the Python programming
+Python 3.14 is a stable release of the Python programming
 language, with a mix of changes to the language, the implementation,
 and the standard library.
 The biggest changes include :ref:`template string literals

Doc/whatsnew/3.15.rst

@@ -46,14 +46,12 @@
    when researching a change.
 
 This article explains the new features in Python 3.15, compared to 3.14.
-
+Python 3.15 was released on 9 October 2026.
 For full details, see the :ref:`changelog <changelog>`.
 
-.. note::
+.. seealso::
 
-   Prerelease users should be aware that this document is currently in draft
-   form. It will be updated substantially as Python 3.15 moves towards release,
-   so it's worth checking back even after reading earlier versions.
+   :pep:`790` -- Python 3.15 release schedule
 
 
 Summary -- Release highlights
@@ -62,7 +60,7 @@ Summary -- Release highlights
 .. This section singles out the most important changes in Python 3.15.
    Brevity is key.
 
-Python 3.15 will be the latest stable release of the Python programming
+Python 3.15 is the latest stable release of the Python programming
 language, with a mix of changes to the language, the implementation,
 and the standard library.
 The biggest changes include
@@ -147,6 +145,7 @@ Release changes:
 
 * :ref:`The official Windows 64-bit binaries now use the tail-calling interpreter
   <whatsnew315-windows-tail-calling-interpreter>`
+* The official macOS binaries now install free-threading support by default
 
 
 New features