Prepare the 2.15.0rc6 release. (pantsbuild#18263)

src/python/pants/notes/2.15.x.md

@@ -96,6 +96,25 @@ These synthetic targets can also be generator targets in order to further create
 [plugin documentation for the Synthetic Targets API](https://www.pantsbuild.org/v2.15/docs/target-api-concepts#synthetic-targets-api)
 for more information.
 
+## 2.15.0rc6 (Feb 16, 2023)
+
+### New Features
+
+* Allow exporting codegenerated files/resources (Cherry-pick of #18236) ([#18241](https://github.com/pantsbuild/pants/pull/18241))
+
+### Bug fixes
+
+* Fix bootstrap issue with `__defaults__` and environments. (Cherry-pick of #18251) ([#18262](https://github.com/pantsbuild/pants/pull/18262))
+
+* Upgrade to Lambdex 0.1.9 (Cherry-pick of #18257) ([#18261](https://github.com/pantsbuild/pants/pull/18261))
+
+* Delete override of expected `exe` name for `shfmt`. (Cherry-pick of #18258) ([#18259](https://github.com/pantsbuild/pants/pull/18259))
+
+* Allow breakpoints to be hit when run_in_sandbox is False (Cherry-pick of #18244) ([#18245](https://github.com/pantsbuild/pants/pull/18245))
+
+### Documentation
+
+* docs: add What's New section for 2.15.x release notes ([#18226](https://github.com/pantsbuild/pants/pull/18226))
 
 ## 2.15.0rc5 (Feb 10, 2023)