Data Prepper 2.15.0 release notes.

Signed-off-by: David Venable <dlv@amazon.com>

Author: dlvenable

release/release-notes/data-prepper.release-notes-2.15.0.md

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+## 2026-04-06 Version 2.15.0
+
+---
+
+### Breaking Changes
+
+
+### Features
+
+* Support Prometheus Remote Write v1 as a source ([#6533](https://github.com/opensearch-project/data-prepper/issues/6533))
+* Add Iceberg CDC source plugin for capturing row-level changes from Apache Iceberg tables ([#6552](https://github.com/opensearch-project/data-prepper/issues/6552))
+* Add S3 Enrich processor to merge enrichment data from S3 into pipeline events ([#5992](https://github.com/opensearch-project/data-prepper/pull/5992))
+* Add substring expression functions: `substringAfter`, `substringBefore`, `substringAfterLast`, `substringBeforeLast` ([#6612](https://github.com/opensearch-project/data-prepper/issues/6612))
+* Add `generateUuid()` expression function for the add_entries processor ([#6653](https://github.com/opensearch-project/data-prepper/pull/6653))
+* Support function composition in expressions ([#6322](https://github.com/opensearch-project/data-prepper/issues/6322))
+
+### Enhancements
+
+* Support server-side encryption with KMS and DSSE-KMS in the S3 sink ([#6528](https://github.com/opensearch-project/data-prepper/issues/6528))
+* Support open source Prometheus in the prometheus sink ([#6594](https://github.com/opensearch-project/data-prepper/issues/6594))
+* Support getting event size via expressions ([#6278](https://github.com/opensearch-project/data-prepper/issues/6278))
+* Mark the SQS sink as generally available ([#6661](https://github.com/opensearch-project/data-prepper/pull/6661))
+* Rename `otel_*` source plugins to `otlp_*` for consistency ([#6530](https://github.com/opensearch-project/data-prepper/pull/6530))
+
+### Bug Fixes
+
+* Fix Prometheus sink NullPointerException when unit or aggregationTemporality is null ([#6683](https://github.com/opensearch-project/data-prepper/issues/6683))
+* Fix error syntax in logs-otel-v1 index template ([#6646](https://github.com/opensearch-project/data-prepper/issues/6646))
+* Fix default dlq_pipeline not receiving failed events from the OpenSearch sink ([#6643](https://github.com/opensearch-project/data-prepper/issues/6643))
+* Fix invalid document version events still included in OpenSearch bulk requests ([#6601](https://github.com/opensearch-project/data-prepper/issues/6601))
+* Fix KMS encryption plugin cache using incorrect key type for lookups ([#6636](https://github.com/opensearch-project/data-prepper/pull/6636))
+* Fix empty plugin configurations failing after Jackson upgrade ([#6598](https://github.com/opensearch-project/data-prepper/pull/6598))
+
+### Security
+
+* requests-2.32.5-py3-none-any.whl: 1 vulnerabilities (highest severity is: 4.4) ([#6690](https://github.com/opensearch-project/data-prepper/issues/6690))
+* aws-cdk-lib-2.241.0.tgz: 2 vulnerabilities (highest severity is: 6.5) ([#6689](https://github.com/opensearch-project/data-prepper/issues/6689))
+
+### Maintenance
+