Section 15. Whoever breaks and enters a dwelling house in the night time, with the intent mentioned in the preceding section, or, having entered with such intent, breaks such dwelling house in the night time, the offender not being armed, nor arming himself in such house, with a dangerous weapon, nor making an assault upon a person lawfully therein, shall be punished by imprisonment in the state prison for not more than twenty years and, if he shall have been previously convicted of any crime named in this or the preceding section, for not less than five years.