Is there any option to Exchange my 2018 15" macbook Pro for 16" Macbook Pro in India?

You can see if this program is available in India:

Apple GiveBack [formerly: Apple Recycling Program; formerly: Apple Trade-up program] - All computer and mobile devices, including non-Aple brands - "Trade in your eligible device for an Apple Store Gift Card. If it’s not eligible for credit, we’ll recycle it for free. No matter the model or condition…" https://www.apple.com/shop/trade-in

You would probably make more selling your old computer yourself.

Considering the fundamental flaw of the keyboards on the 15" MacBook Pro models one would think that Apple would institute some sort of special exchange program to remedy the grievances of loyal customers who own these faulty units. The standard trade-in scheme is not applicable in this scenario.