GSTR 9C form

Interest income is exempt under section 12/2017.

Section 2(112) “turnover in State” or “turnover in Union territory” means the aggregate value of all taxable supplies....and exempt supplies

Section 35(5)Every registered person whose turnover during a financial year exceeds the prescribed limit shall get his accounts audited by a chartered accountant or a cost accountant.

Thus interest income is to be considered to determine turnover for 9C(audit)