No appropriation, purchase or lease shall be made pursuant to the preceding sections whereby any incorporated town shall within any period of three years obligate itself to pay in the aggregate any sum exceeding one and one-half mills on the total of the assessed valuation of all property, offices, professions and persons in the town upon which town taxes are levied without consent of the majority of the electors as hereinafter provided. No such election shall be required in any case where the question of the increase of the indebtedness of the town for any of the foregoing purposes shall have been submitted to, and assented to, by a majority of the electors of the town voting on such question at an election held according to law.