[Debugging]How will you identify what is wrong with the model and in which part?

I encountered one interview question:
Suppose you have: browser–>cache–>database model.Now,suppose a bug fix has been done on this model.After bug fixing, it has been found that a request–.>response that earlier took 1ms now takes 25 ms. How will you identify what is wrong with the model and in which part?

My Approach: I will see the stack Trace.That is sequence of method calls,which method calls which method and further measure the duration of each method call to find out which method took more time(database response,request etc) .Is there any other better alternative possible?