Section 15. Any such corporation may amend or alter its articles of organization in the manner provided by sections seventy to seventy-two, inclusive, of chapter one hundred and fifty-six B, so far as applicable; provided, that such amendment or alteration shall require a vote of three-fourths of the members present and voting at a meeting of the corporation called to consider such amendment or alteration, or if the vote upon such amendment or alteration is taken by mail, by vote of three-fourths of the members who return votes. A vote by mail upon such amendment or alteration shall not be valid unless votes are returned by at least three fifths of the members of the corporation.