Honestly I don't think you have any chances. Tenant moved out before due date but didn't officially turn in the keys. There is no reason for you to go in earlier than 11/15. I bet you didn't try to contact the tenant before going in the property. Theoretically speaking, the tenant could go back any time before 11/15 and clean up the mess.
I think the tenant was being very reasonable and only asked for part of the rent back and deposit. However it's your house and you do whatever feels right.