docs: release notes for the v20.3.15 release #2895

Job	Run time
list	37s
workflow (build-cli)	1m 46s
workflow (build-unit-tests)	2m 32s
workflow (devkit-core-tests)	1m 28s
workflow (devkit-core-tests-rerun)	1m 39s
workflow (modules-builder-tests)	1m 53s
	9m 55s

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