Section 61. A mortgagee holding a first mortgage or lien on a dwelling house located in the commonwealth of 4 or fewer separate households occupied or to be occupied in whole or in part by the mortgagor who requires advance payments, deposits or other security by the mortgagor for the payment of real estate taxes on mortgaged property, shall pay interest to the mortgagor on any amount so paid or deposited in advance. Interest shall be paid at least once a year at a rate and in a manner to be determined by the mortgagee. Mortgagees showing a net loss from the investment of the amounts so paid or deposited may file with the commissioner of banks a request for an exemption from the requirement that the interest be paid to mortgagors.