If I may join the merry speculation whirligig, I would like to submit two theories:
1. The WS-15 has not yet been installed in an aircraft and has not been shown publicly as a whole. However, the *nozzle* with which it will eventually be fitted has - though not necessarily while installed in *an actual J-20*. It might be that the WS-15 is intended to receive the con-di 3D-TVC design which has been seen flying in that J-10 testbed, as Hyperwarp & Hendrik have suggested. Although the engine in this case is a WS-10, that's not an unprecedented scenario - the LOAN nozzle for the F135 on the F-35 was first flight-tested with a F100 in a F-16. Gist: as soon as that AVEN-like design appears on the J-20 we'll know it's the WS-15.
2. The WS-15 has not yet been installed in an aircraft and has not been shown publicly as a whole. However, the *nozzle* with which it will eventually be fitted has - though not necessarily while installed in *an actual J-20*. Perhaps Salut of Russia is contributing to the WS-15 project and it's the low-observable 3D-TVC design which was shown several months ago? A problem with that hypothesis is that Salut's nozzle has considerably more than 15 petals, with the caveat that the external aerodynamic/RCS shroud was never shown. Then again on what basis are we so certain that 15 is in fact the number to look out for? As far as I understand, gongke did not specify he WS-15's petal count - only that it differs from both the AL-31F and the WS-10 variant currently flying in the J-20.
Both options fit with the elaborate explanation of the original source which latenlazy has so kindly provided.
If Gongke was referring to the J-10’s TVC nozzle then he wouldn’t be afraid of sharing a picture of the nozzle since that nozzle is already out in the open.
That's not necessarily how secrecy/classification works. The nozzle design itself might well not be a secret, while its association with the WS-15 and J-20 is very much so. Provided that you maintain plausible deniability, things can be hidden in plain sight by merely not telling the whole story. Conversely, publicly known facts may still be officially classified, simply because the rules governing that status require that they are to be considered secret. It's a bureaucratic stamp at the end of the day, and subject to all of the absurdities that can entail.
Officially the F-117 is retired and grounded - yet several examples are still routinely seen (and photographed) flying around the restricted areas of Nevada in plain daylight. No particular effort is apparently made to hide their presence from outside observers, yet if you were to ask a USAF official, he would steadfastly deny it.
Another famous example is the 1993 shoot-out between Red Army Faction terrorist Wolfgang Grams and German GSG-9 special forces in Bad Kleinen - several witnesses had seen two people accompanying Grams, but official statements only mentioned one (fellow terrorist Birgit Hogefeld). The reason for the discrepancy (which gave rise to various conspiracy theories)? In fact the third person did exist, but he was an undercover agent whom government authorities sought to keep a secret (firstly out of concern for his personal safety, secondly to hide the fact that they had been able to infiltrate the organisation). It was some considerable time before they came round to the seemingly trivial fact that he was not going to be "un-seen", and acknowledged his presence.
Just posting a small addendum because I’m past the 20 minute time for edits. One could have also seen the nozzle design without having seen it installed on the J-20.
Exactly.
