Paid a sum of 15 lacs on trust for a property. Betrayed!

An acquaintance wanted to sell an under construction property as he was in immediate need of funds. We agreed to buy and paid him 15 lacs with the agreement noted and signed on a paper. Not a formal agreement. This may have been the mistake. It has been almost two years now and he is neither transferring the flat to our name nor paying back. The hand written agreement has his signature and that of two witnesses along with details of cheques via which the amount was paid to him and how the transaction for remaining amount was to be carried out once the property transfer was done. The guy has been escaping calls and skipping meetings. How can I recover the amount? Can I file a law suit? Are the cheque details and the hand written agreement enough evidence to sue him? Can I file a case of betray of trust and mental harrasment? We are not really rich to let go of this big an amount or afford to let it remain stuck like this for such a long time. Need some suggestion on how to deal with this situation.