Well dude maybe you have trustworthy source of this information, but I remember K3S which has Su-30MKK got 4 "Golden Helmets" in PLAAF last year.
Besides, even you are right about J-10 won the fight against Su-30MKK, it cannot states that "J-10C is much better than J-15": first of all, Su-30MKK is a multifunctional fighter, and J-10, however, more focus on Air. Second, Su-30MKK uses old Russian N001VE radar and elect equipment, it is worse than Chinese radar on J-10A, J-11B and J-15, not to mention J-10C, which is carrying China's best equipments including AESA now.
I really cannot understand why the performance of Su-30MKK can inform the situation of a totally different plane J-15? They all come from a same prototype, yes, so what? Their mission, frame, equipments are all different. I am pretty sure that even J-10A can easily beat earliest version Su-27, does it mean that J-10A can beat Su-35?
Just like I said, J-15 is still upgrading, and its equipments are better than Su-30MKK, they maybe similar to the equipments on J-11B. After all, it is unfair to say entire J-15 and its future type are worse than the latest version of J-10. Even if J-15 lost the battle against J-10 with same level radar and equipments, we still need to consider conditions like pilots and air situations, those fights' result never caused by a single reason.