Under Consumer Protection Act, 2019 a tenant is consumer. Issue a lawyer's notice to landlord seeking payment of 15K unlawfully deducted with interest. After that file a complaint in District Consumer Forum under new Consumer Protection Act, 2019 under which proceeding are very fast. You will get refund with interest, compensation for mental harassment, cost of complaint and lawyer’s fee. For filing above case you will incur 5K expenses. It is not the question 15K but it is violation of your right. Any Advocate can file case in District Consumer Forum, you need not appear in the Forum, everything will be taken care by Advocate. But you not only get back 15K with interest, you can easily get around 30K and landlord will learn a good lesson.