Does the rent for the additional fifteen days remain owed by the tenant, or is it excused given that it is customary and the amount is small?

The tenant is not allowed to remain in the property after the expiration of the lease except for a valid excuse, in which case he must pay the fair market rent (ujrat al-mithl). If the term expires and there is unharvested crop in the land, it is left until it is harvested, for the fair market rent. If the tenant exceeds the agreed-upon period or distance, he is liable for the mentioned rent and the fair market rent for the excess. The tenant is obligated to pay the rent for the additional period, unless custom dictates overlooking it, in which case custom is considered tantamount to a stipulated condition.