The Commissioner by order summarily may postpone or suspend the effectiveness of the registration statement pending final determination of any proceeding under § 11-511 of this subtitle. On the entry of the order, the Commissioner promptly shall notify each person specified in § 11-513 of this subtitle: That it has been entered; The reasons for its entry; and That within 15 days after the receipt of a written request the matter will be set down for hearing. If a hearing is not requested and one is not ordered by the Commissioner, the order will remain in effect until it is modified or vacated by the Commissioner. If a hearing is requested or ordered, the Commissioner, after notice of and opportunity for hearing to each person specified in § 11-513 of this subtitle, may modify or vacate the order or extend it until final determination.