In law, one word has one definition but many meanings. So a person needs to understand the whole context of the matter to understand the meaning of one word.
Let me describe your question here.
You purchased a property having price of Rs. 15,00,000/-
You borrowed (not home loan) Rs. Rs. 15,00,000/- (interest rate is a question)
But the agreement had a price of only Rs. 100,000/-
You held the property for more than 36 months.
Now you are selling the property for 'X' amount
So the market price is Rs. 15,00,000/- and the stamp duty paid was on Rs. 100,000/-
I am assuming the large part of payment made was in cash.
Your question is whether the cost of acquisition shall be Rs. 100,000/- or Rs. 15,00,000 + interest paid.
Please confirm.