The F-14 is a decent comparison, as it was originally intended to use the F100 (F401 technically) engine but settled for TF30s instead, before eventually installing the F110 later on.
But one possible difference between the F-14's engine situation from the J-20, is that J-20 probably will always have WS-15 as the intended engine whereas the original intended engine for the F-14 (F100) was discarded during development for the TF30s and a better engine was only procured in the form of the entirely different F110 later on.
There is no alternative to WS-15 for the J-20, so it is virtually guaranteed that the J-20's eventual intended engine configuration will be with the WS-15.
While I fully agree Blitzo, I would remind all that the WS-15 is very much an unknown quantity, at what stage in development, so far as we know, it has flown only on a transport aircraft pylon?? So, I at one time made the statement that the J-20 might well fly with the F-117??? as an interim powerplant, it is possible, but is it likely??? and as to the SU-35 being bought as an interim??? it is possible, but is it really going to happen??? I am as skeptical as my friend the engineer, I think he remains very much in touch with the pulse of the PLAAF.
As I stated, the J-20 is presently at the head of her class, I believe it is very important that China continue to fully support this class leading aircraft, and do what is necessary to bring it up to speed. I say that as a friend and admirer of the Chinese people, Chinese ingenuity, and one hopeful of a better relationship long term with China. If our relationship as nations were to go south, I would be very disappointed, and not be as supportive of the J-20??? but I would still be a big fan of the Chinese people whom I love and care about.
Remember, my 5th birthday was on Okinawa, the big treat in my early life was lunch after church at the Chinese restaurant at the CAT terminal. I have had Asian friends my whole life, one day a week "Yashi-Co" came to our house, did laundry, ironed, and played Momma, she was a sweety, and I loved her dearly! Our whole family thought very highly of her, she was sweet, respectful, and worked very hard, and I have no doubt she loved not only me, but my rotten brother "JIM"!
Oh, and I still love going to the "Chinese Restaurant", Mr Yan was the egg-roll king! nobody else will ever come close.