Update CHANGELOG

Author: fantavlik

CHANGELOG.md

@@ -1,5 +1,18 @@
 # Splunk Enterprise SDK for Python Changelog
 
+## Version 1.6.15
+
+### Bug fixes
+[#301](https://github.com/splunk/splunk-sdk-python/pull/301) Fix chunk synchronization
+[#327](https://github.com/splunk/splunk-sdk-python/pull/327) Rename and cleanup follow-up for chunk synchronization
+[#352](https://github.com/splunk/splunk-sdk-python/pull/352) Allow supplying of a key-value body when calling Context.post()
+
+### Minor changes
+[#350](https://github.com/splunk/splunk-sdk-python/pull/350) Initial end-to-end tests for streaming, reporting, generating custom search commands
+[#348](https://github.com/splunk/splunk-sdk-python/pull/348) Update copyright years to 2020 
+[#346](https://github.com/splunk/splunk-sdk-python/pull/346) Readme updates to urls, terminology, and formatting
+[#317](https://github.com/splunk/splunk-sdk-python/pull/317) Fix deprecation warnings
+
 ## Version 1.6.14
 
 ### Bug fix