Section 15. Should the gross receipts of any such corporation from the operation of a project undertaken by it under authority of this chapter, in any year exceed (1) operating and maintenance expenses together with such reserves as are necessary to create a fund to replace furnishings and worn-out equipment, including any ground rents or other payments under any lease, (2) taxes and fees, (3) interest on mortgages and other indebtedness, (4) premiums, fees or other charges or expenses incurred in connection with the insurance or guaranty of any mortgage or the insurance or guaranty of any annual return from a project, including any amounts payable to the Federal Housing Administration or any other agency or instrumentality of the United States for such purposes, (5) amortization, in accordance with the provisions of any schedule, plan or method of amortization described in any application submitted to the housing board under section five of this chapter, or in any schedule, plan or method of amortization subsequently submitted to and approved by the housing board, (6) dividends, (7) authorized transfers to surplus or reserves, and (8) other payments authorized or approved by the housing board, the amount remaining shall be applied to the payment to the city or town in which the project is located of the amount, if any, by which the taxes would have been assessed upon the real estate and tangible personal property of the corporation in such year if such real estate and tangible personal property had not been exempt from taxation, exceeded the excise paid by such corporation and distributed to such city or town in such year under section ten.

The balance, if any, may, subject to the approval of the housing board, be applied in whole or in part to reducing the indebtedness of such corporation, to renovating or to improving the property, as by installing additional facilities for the use of tenants, to the acquisition and development of additional property which shall be subject to the same control and regulation as the original project.

The charges for operation and maintenance may include insurance and reserves essential to the management of the property or necessary to meet requirements for depreciation and amortization of bonded indebtedness, but the amount set aside therefor shall be subject to the approval of the housing board. Nothing in this chapter shall be construed to obligate the commonwealth, or to pledge its credit, to any payment whatsoever to any such corporation or to any stockholder, bondholder or creditor thereof.