Is the notice for rent increase legal if served to the tenant 60 days before contract expiry?

We received a letter (4 to 5 months before the contract ended) from the landlord showing the intention of rental increase as per the rental index along with admin charges.

The letter didn't state the actual amount that would be increased (it's a physical letter given to us by building security).

Now less than 60 days to the end of the contract we get a letter mentioning a 15% increase which is the max as per the index.

My question here is whether the rent increase is valid as the actual increase was conveyed post the 90 days period?

The second question, if we don't agree with the new rent, will my contract auto-renew as per old rent or new rent?