HI,
if your interest income in more then Rs 2.5 lakhs but after deductions under chapter VI it is falling below taxable limit. then there is no need to file return.
you need to check your income tax site , if income tax authorities has raised any demand or sent you any intimation.
I would suggest you to file IT return for FY 2015-16 & 2014-15, and if any query raised by the assessing officer then you can act accordingly.
if your taxable income is within 10%or 20% or even 30% tax slab then there would be no tax liability due from your end as TDS rate of deduction for NRO is 30%. it might be possible you get some refund.
and if there is no tax liabilty then there would be no interest charges or penalties arises.