15.—(1) No will, or any part thereof, which has been revoked is revived otherwise than by—
(a)re-execution of the revoked will; or
(b)a codicil showing an intention to revive the revoked will.
(2) Where any will which has been, first, partly revoked, and later wholly revoked, is revived, the revival does not extend to the part revoked before the revocation of the whole will unless an intention to revive that part is shown.