Answer: You should code repair of nasal septal perforations with 30630 (Repair nasal septal perforations). According to the Coders- Desk Reference, this involves the creation of local mucoperichondrial flaps on either side of the perforation with a scalpel. Each flap is designed to expose one side of the septal cartilage while retaining mucosal coverage of the septal cartilage of the opposite side. The flaps are sutured in a single layer to cover the perforation. This description matches your otolaryngologist's notes.
The codes that you mention describe microvascular flaps: 15740 is an -island pedicle- flap, and 15750 is a -neurovascular pedicle- flap.