You don’t need to worry about Form 15 or Form 16 at the time of applying for the Encumbrance Certificate. EC’s are always applied for a fixed time-period. For example, you want to see the transactions that have happened in the last five years for a particular property, then you will have to apply for the EC for that duration. If transactions are found during that period then you will be issued the EC as Form 15 with all the details of the transaction. If no transactions are found then you will be issued the EC as Form 16 also called a Nil Encumbrance Certificate.