Actions to foreclose real estate mortgages

Except where, in special cases, a different limitation is prescribed by statute, a civil action for the foreclosure of any real estate mortgage by action or by advertisement can be commenced only within fifteen years after the cause of action shall have accrued, and said period of fifteen years shall not be extended by nonresidence, legal disability, partial payment, or any new promise; provided, however, that the term "new promise" shall not be deemed to embrace an extension of a mortgage duly executed and recorded as contemplated by §