Fix known issue docs for elastic#111866 (elastic#111956)

The `known-issue-8.15.0` anchor appears twice which breaks the docs
build. Also the existing message suggests incorrectly that
`bootstrap.memory_lock: true` is recommended.

Author: DaveCTurner

docs/reference/release-notes/8.15.0.asciidoc

@@ -16,7 +16,11 @@ after it is killed up to four times in 24 hours. (issue: {es-issue}110530[#11053
 * Pipeline aggregations under `time_series` and `categorize_text` aggregations are never
 returned (issue: {es-issue}111679[#111679])
 
-* Elasticsearch will not start on Windows machines when the recommended [bootstrap.memory_lock: true](https://www.elastic.co/guide/en/elasticsearch/reference/current/setup-configuration-memory.html#bootstrap-memory_lock) setting is configured due to [native access refactoring](https://github.com/elastic/elasticsearch/pull/111866). The workaround for 8.15.0 is to downgrade to the previous version.  This issue will be fixed in 8.15.1.
+* Elasticsearch will not start on Windows machines if
+[`bootstrap.memory_lock` is set to `true`](https://www.elastic.co/guide/en/elasticsearch/reference/current/setup-configuration-memory.html#bootstrap-memory_lock).
+Either downgrade to an earlier version, upgrade to 8.15.1, or else follow the
+recommendation in the manual to entirely disable swap instead of using the
+memory lock feature (issue: {es-issue}111847[#111847])
 
 [[breaking-8.15.0]]
 [float]