The Part B Procedures 2.35.2.15 says -700: Use normal procedures and reference speeds unless a Flap 15 landing is planned. So it is not just in the event of a leading edge device problem that you may use Vref ICE. For example, all 737 one engine out landings are made with Flap 15. The best way to do this is on the FMS Approach page when you select the Flap 15 approach speed, simply amend the line to read 15/(approach speed +10).
The NG Vref ICE differs from the Classic 737 and Vref ICE is used for any Flap 15 landings ONLY, no others.