P15A & P15B are sem2sem overall and are different from P15 Delhi class.
Originally P15A was supposed to be a direct derivative of P15 with Ruskal armaments and Radar, but then the Admirals discovered THE JEWS who were selling a large fancy MFSTAR radar with big range and no spinny mechanical parts with CEC capability( missile from ship B can be fired at enemy missile/jet etc being tracked by ship A that can be kilometers away ) and long range vertically launched MRSAM missiles with 70km range as opposed to the Ruskal's spinny Fregat radar( later exposed as having some defects ) and 50km shtil-1 combo.
Jooz were also giving out the Tee Oh Tee necessary for the missiles to sell this to the baboos and mantris and DPSU lobbies also.
Needless to say, upon witnessing the Jewish radar and missiles giving "western" high-tech capabilities at a fraction of the cost, the plan to integrate Cold War Soviet vintage ((( export quality ))) stuff was junked and P15A was redesigned into the current version, which is the navy standard( Nilgiri, P17B, NGC ) now, reduces logistical problems of having a diverse zoo of equipment like the other two forces have, also gives them a tech advantage over the Bhikari Mulq next door
Navy standard for modern ships is
>76mm SRGM
>30mm AK630 CIWS
>Barak 8 VLS SAM
> brahmos
>MFSTAR
>LW-08 radar being upgraded to LANZA-N
>Those rocket depth charge things, forgot what they are called.
>deshi torpedo launcher, chaff and decoy launcher
You don't need a ((( fresh design ))) for everything, making derivative designs until your requirements demand you move to a fresh design is a good practice