Your query compels me to doubt whether your opening statement is correct.
Firstly, if you can say that your gross salary is Rs.15500-00 ( should be per mensem though not mentioned so ), it should certainly comprise of different components in which case there is no necessity to ask about basic and if it is a lump sum, then it should be consolidated salary warranting your question about the basic salary.
Secondly, in the absence of other benefits you get which can be computed in terms of money and the amounts of employer's contributions to EPF,ESIC,Gratuity Fund etc., one can not arrive at the actual amount of your CTC.
28th August 2018 From India, Salem
30th August 2018 From India, Bengaluru
As per rules, salary is required to be mention in the appointment letter whereas CTC is not mandatory to be mentioned.
It is not clear as to what facilities are being provided to you by employer--say free meal/ subsidized meals, free pickup and drop etc--which all will go in calculation of CTC.
Why not ask HR to provide you same ?
31st August 2018 From India, Delhi