There is no rule and procedure for set off TDS liability for two alternate year by the assesee, so in this case Claim refund in AY 2011-12 and pay Rs15 lacs along with Interest if any in AY 2012-13.
You meet the TDS Officer of your range or ward and explain him the situation. Now a days, the A.O. has the power to rectify the details once. The details that can be rectified are: the Code under which the payment is made, the Assessment Year, Type of Payment. It has already happened with one of my clients and the TDS Officer has even corrected it by using his code. Ask him he will surely help you out.