You may show the agreement, appointment letter, certified standing orders of the company to a competent and experienced labor consultant/service lawyer.
Your lawyer may opine that the contract is in violation of standing orders of the company or void, illegal, arbitrary, inequitable and legally unenforceable.
Employee should always consult elders in the family, competent and experienced well wishers, trained legal mind amongst acquaintances, lawyer/law firm before signing on the dotted line. It is always better to consult than to repent later.
You should have avoided abandoning the job. You should have pin pointed the misconduct on the part of employer and declared him unworthy of being employed with.
You have given the employer an opportunity to smell 15 Lacs without investing a single penny and now he is chasing you. The employer shall always claim that his actions are not illegal and are in accordance with terms of contract signed by you.
Approach your lawyer and submit fitting reply or proceed as per expert advice of your lawyer.
In the meantime you may find the attachments useful.