Usually, the interest rate of second-home mortgage cannot be lowered, because the mortgage interest rate is stipulated by the state, and the interest rate standards implemented by banks are the same. Therefore, even if the first house has paid off the loan, it will not have any impact on the loan interest rate of the second house.
Please note that the specific mortgage interest rate may be different due to bank policies, local housing market conditions and other factors. It is recommended to consult the bank staff to obtain the latest mortgage interest rate information.