Look at the nozzles of this engine, and compare it to the J-20's silver engine petals unfolded out like this -- they're identical. Unless this is a PS, I'm thinking this is the J-20's current engine (or at least engine nozzle at any rate) which we are looking at.
I guess this is an engine we don't know about then? A WS-10X?
Also, has anyone found it a little odd that we haven't heard news of the WS-15 in a very long time? (Except for that very long report which I think sounded kinda bogus)