Introduction:
Project 15B, also known as the Vishakhapatnam Class, is a class of guided-missile destroyers built for the Indian Navy. These destroyers are designed to be stealthy and have advanced weapon systems. In this question, we are asked to determine the number of ships commissioned under Project 15B, including INS Surat.

Details:
The correct answer is option 'B' - 3.
Below are the details explaining why option 'B' is the correct answer:

INS Vishakhapatnam:
1. INS Vishakhapatnam is the lead ship of the Vishakhapatnam Class of destroyers.
2. It was launched in April 2015 and is currently undergoing sea trials.
3. Once the sea trials are successfully completed, INS Vishakhapatnam will be commissioned into the Indian Navy.

INS Mormugao:
1. INS Mormugao is the second ship of the Vishakhapatnam Class.
2. It was launched in September 2016 and successfully completed its sea trials.
3. INS Mormugao was commissioned into the Indian Navy on 7th November 2020.

INS Imphal:
1. INS Imphal is the third ship of the Vishakhapatnam Class.
2. It was launched in April 2019 and is currently undergoing sea trials.
3. Once the sea trials are successfully completed, INS Imphal will be commissioned into the Indian Navy.

INS Surat:
1. INS Surat is the fourth ship of the Vishakhapatnam Class.
2. It was launched in October 2021 and is yet to undergo sea trials.
3. As per the question, INS Surat is included in the count of commissioned ships under Project 15B.

Conclusion:
Based on the information provided, there are currently three ships commissioned under Project 15B (Vishakhapatnam Class) destroyers, including INS Surat. These ships are INS Vishakhapatnam, INS Mormugao, and INS Surat.