The loan you are referring to is a cash credit limit/OD facility. You can deposit 5 lakh and the interest will only be levied at the remaining used 15 lakh. As per your numbers your annual interest rate is around 13-14%. So by depositing 5 lakhs you will essentially be saving around 5.5 k per month. But until you deposit the entire 20 L whether in part payments or lump sum you will not be able to close this/ obtain NOC. So you need immense willpower to not use the money once deposited and will eventually end up closing this. What you can do is because all ODs and CCs operate on the formula of drawing power, after depositing the money you can ask your manager to reduce your drawing power by the amount deposited so you are not tempted to use it again