Unregistered lease deed - 15 years - valid or not

Dear Experts, Kindly clarify my query ,

I own a shopping complex in Tamilnadu and letout to private sector chit fund limited for a period of 15 years 2010 to 2024 by the way of unregistered lease deed.

Recently I came to know that sec 17(1)(d) of Indian registration act 1908 lease period above 11 months are not valid. Hence I was forced to undergo lease deed by my advocate.

I wish to state that there is a friendly relationship between manager and myself.

My query :

1. Registration for above leased property is mandatory or not.
2. If unregistered lease deed is not valid for 15 years. Shall I make a fresh registrated lease deed with new terms and conditions.

Thanks in Advance