from what i found:
comparing j-15(i took su-33) and mig-29k:
1.j-15 is in overall a big plane,with
height of 5.93m v/s 4.40m of mig 29k,
wing area of 62.0m2 v/s 43.0m2 of mig 29k
for a carrier based jet,these matters a lot since smaller planes will be easier for storage,transport etc.
2.j-15 leads in case of maximum take off weight,
with 33,000 kg (72,752 lb) v/s 24,500 kg (54,000 lb) of mig 29k.
3.mig-29 k has a better power-to-thrust ratio 0.97 v/s 0.83 of j-15
4.j-15 has more hard points than mig-29k i.e
12 v/s 9 of mig-29k
5.as for the cannons,both carry the same type of cannons,but j-15 can carry more ammunition i.e,150 v/s 100 rounds