Now comparing Mig 29K with j 15.
I think India made a very good decision to go with Mig 29k, because the only back draw is the payload capacity of mig 29k 5.5 ton as against 8-9 ton of j 15. Rest all stands in favour of Mig 29K.
1. Avionics: Mig 29K is considered 4++ generation fighter because of it's modern avionics which is way superior than j 15 or original Su 27K or Su 33.
2. RCS : Mig 29K has reduced RCS because of the extensive use of composites and slightly change in design. It's maker believe that it's RCS is reduced by 5 times compared to the earlier version of Mig 29 which has RCS in 3.5-4.5 m square range.Thus, it's RCS is in the range of 0.7 - 0.9 m square.
3. RADAR: Radar fitted with Mig 29K can detect an enemy of RCS 5m2 from 150km away and track from 120km away. Considering 10m2 RCS of j 15, it will able to detect it from 200km-240km away and start tracking it from 160km-190km away and can detect naval frigates and destroyers from 300km to 400km away whereas j 15 will able to detect naval ships from very same distance but has the capability of detecting fighter of 1m2 RCS from 90km-100km away and can track it from 80km-85km away.
4. Weapons: Mig 29K can carry all the present modern A2A and A2G missiles and the wide variety of weapons it can is more than that j 15 can carry as j 15 can't carry R 77 missiles and in addition to that Mig 29K will be able to carry smaller version of Brahmos with satellite navigation which has just enter for development.
(Note:- I am not considering the combat radius of Mig 29K(700km-800km) to that of j 15(1000km-1100km) owing to the fact for naval operation fighter goes max to 500km-600km away from their carriers as this is considered sufficient distance. All modern day naval fighters in operation have the similar kind of combat Radius.)