Wouldn’t you say assuming that the J15 has the same range as the Su33 is exactly the kind of baseless pulling figures out of thin air assumption you are warning against?
Sure, that's why I am asking for a source. What source mentions J-15 range at all? And once we establish a decent source, then we can talk about exact numbers. Until then, we can either A) not talk about J15 range. or B) sort of assume it's similar-ish to Su-33 but that doesn't help us much as the term "similar" may mean different stuff to different people. Plus there are always people who believe it's not even similar but somehow much different.
Would J-15T have more range and payload? Or are we assuming that J-15 can carry full payload full fuel tank already?
Su-35 has much longer range than su-30, is that true?
Su-33 is quite old, I would not be surprised if some work can be done to give it more range or payload. Whether those work has been done, I didn't know.
It's not about being old, it's about 3 factors: Weight. Fuel carried. And fuel consumption.
Fuel consumption is, right now (i am not talking about years into the future with some different engines) rougly comparable to su33 because engines are comparable.
Fuel carried? Well, we know what Su-35 increased the fuel load of Su-27 from 9.4 tons to 11.2 tons. And did it increase range over su-27? No, it remained roughly the same. Because Su-35 is heavier (by 2.6 tons) and thus its engines, even though they're more modern, are in real world situation using up more fuel.
So, it's certainly possible that J15 (and any other modern Chinese flanker after) also carry more fuel. Maybe 10 tons. Maybe 11 tons. Who knows. But at the same time, modern construction methods offer fairly miniscule savings in weight, while expanded roles and requirements generally increase weight. That's why Su-33 weighs as much as a Su-35. Now, J-15 may indeed weigh a bit less. But there's no way to tell how much less.
One could guesstimate a range of figures for an expected ferry range of J-15 using all the above but it'd still be just a wild guess. What I'd prefer is a credible source.