It seems that stating that "we know nothing" is the most accurate statement when talking about the WS-15. It seems that no one knows for certain, how along it is in development, if it has been tested inflight. It could even be in "development hell". The fact that J-20 is now flying with WS-10 doesnt help to dispel that idea.What you and everybody else found about WS-15 is not spec from any official or designer's source, the "likely specs of Izd.30" means it is not official either. This simply means that nobody knows, all being talked about are perhaps and maybes.
I think it is better that we say "we know nothing" than speculation about any of the engines.