No, a threat to commit suicide can not be termed as coercion. But further, it also depends upon the situation. A well-known example is the case of Ammiraju v. Seshamma, who threatened to commit suicide in order to force his wife to release the property which amounted to coercion. His wife was prejudiced and it can't be forbidden by law. But under section 15, a mere prejudice cannot provide relief to a person.