An initial principal sum of Rs. 8000, invested by Pranav, accrued interest at a compound rate of 20% annually for a period of 2 years. Subsequently, the entire sum, compounded with the interest, was redeployed into an account offering simple interest at an annual rate of 15% for an additional 2 years. Calculate the cumulative interest earnings that Pranav accrued over the comprehensive 4-year period.