Delay payment int. by builder @15% but peanuts for builder delay

I purchased a flat from Mahindra Bebanco, Mihan, Nagpur. There was delay of payment from my side and the builder charged me interest @ 15%. Builder says It is mentioned in the agreement and I need to abide by the agreement. Now there was a delay of 9 months from builder side. I pointed this out to the builder. The builder again refereed me to the agreement and said. 1. 6 months delay builder is supposed to give no compensation. 2. Delay beyond six months builder pay @ 5 Rs. sq. ft. as compensation. It amounts to 6-7K per month and total goes to 21-22K. Now when there is a delay I get compensation in fraction % (based on 22K) and on my delay builder charging me in lacs?? And every discussion I make I am been referred to the agreement document. I have gone through some cases where court/forum has set aside the agreement T&C. But has something changed from then and now which will make my case weak? Can I fight legally with the builder as he is a very big name (Mahindra & Bebanco) who will have battery of lawyers at their disposal?