Placeholder for enterprise release notes (#27295)

Author: anwittin

CHANGELOG.md

@@ -2,6 +2,25 @@
 - [v1.0.0 - v1.9.10](CHANGELOG-pre-v1.10.md)
 - [v0.11.6 and earlier](CHANGELOG-v0.md)
 
+## 1.15.9 Enterprise
+### May 30, 2024
+
+CHANGES:
+* auth/jwt: Update plugin to v0.17.3 [[GH-27063](https://github.com/hashicorp/vault/pull/27063)]
+* core: Bump Go version to 1.22.2.
+
+IMPROVEMENTS:
+* secrets/pki (enterprise): Disable warnings about unknown parameters to the various CIEPS endpoints
+* website/docs: Add note about eventual consietency with the MongoDB Atlas database secrets engine [[GH-24152](https://github.com/hashicorp/vault/pull/24152)]
+
+BUG FIXES:
+* activity (enterprise): fix read-only storage error on upgrades
+* core: Address a data race updating a seal's last seen healthy time attribute [[GH-27014](https://github.com/hashicorp/vault/pull/27014)]
+* pki: Fix error in cross-signing using ed25519 keys [[GH-27093](https://github.com/hashicorp/vault/pull/27093)]
+* replication (enterprise): fix "given mount path is not in the same namespace as the request" error that can occur when enabling replication for the first time on a secondary cluster
+* secrets/transit: Use 'hash_algorithm' parameter if present in HMAC verify requests. Otherwise fall back to deprecated 'algorithm' parameter. [[GH-27211](https://github.com/hashicorp/vault/pull/27211)]
+* ui: Fix KVv2 cursor jumping inside json editor after initial input. [[GH-27120](https://github.com/hashicorp/vault/pull/27120)]
+
 ## 1.15.8 Enterprise
 ### April 24, 2024