Add 2.15 release notes (#1569) (#1570)

(cherry picked from commit 3552e7a)

Signed-off-by: Chase Engelbrecht <engechas@amazon.com>
Signed-off-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>
Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

release-notes/opensearch-alerting.release-notes-2.15.0.0.md

@@ -0,0 +1,15 @@
+## Version 2.15.0.0 2024-06-10
+Compatible with OpenSearch 2.15.0
+
+### Maintenance
+* Increment version to 2.15.0-SNAPSHOT. ([#1543](https://github.com/opensearch-project/alerting/pull/1543))
+
+### Bug Fixes
+* Reduce log lever for informative message. ([#1218](https://github.com/opensearch-project/alerting/pull/1218))
+* Update cron-utils. ([#1503](https://github.com/opensearch-project/alerting/pull/1503))
+
+### Enhancements
+* Add start_time and end_time to GetAlertsRequest. ([#1551](https://github.com/opensearch-project/alerting/pull/1551))
+
+### Documentation
+* Added 2.15 release notes. ([#1569](https://github.com/opensearch-project/alerting/pull/1569))