[release-notes] Release notes 7.15.0 on 7.15 branch (#6006)

Co-authored-by: Mpdreamz <[email protected]>

Author: github-actions[bot]

docs/release-notes/release-notes-7.15.0-generated.asciidoc

@@ -4,6 +4,7 @@
 === Uncategorized
 
 - * Support PIT, Fields and RuntimeFields on AsyncSearch https://github.com/elastic/elasticsearch-net/pull/5989[#5989]  (issue: https://github.com/elastic/elasticsearch-net/issues/5988[#5988])
+- * Add missing properties to AsyncSearch response. https://github.com/elastic/elasticsearch-net/pull/5997[#5997]  (issue: https://github.com/elastic/elasticsearch-net/issues/5988[#5988])
 
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