@medengconfused I think what you are looking for is "Real Returns". At 7% inflation, 1,00,000 15 years ago is equal to 2,70,000 today. You have to calculate at what CAGR 2,70,000 becomes 5,50,500 in 15 years.
So solve for r in the below equation:
5,50,000 = 2,70,000 (1 + r/100)15
The answer...