@VivekP01 The performance of the API can depend on a lot of factors (volume of data, frequency of traffic etc), but calling the same API hundreds of times for every single attribute might not be the best approach.
If your data has common elements, then perhaps they can be grouped into a separate API, and called only once through an asynchronous Job scheduler.
Some other options are :
---- Make the API calls in an off-peak hour and storing them in a Data page for usage later.
---- Make the calls once for every operator instead of calling it per thread.
Maybe filling in the below details will help answer this question better :
--- How many fields are we talking about ?
--- Does the API have to called per case ? Does it pass case specific data ?