ADUM347* Vreg Voltage

We are developing a +-15 volt supply around the ADUM3473, but have a questions regarding the Vreg voltage.  If we configure the voltage divider resistors to a Viso voltage of 16 to provide sufficient headroom for downstream 15 volt LDOs, would this be too far outside the Vreg range of operation for long term use?  If so, would the ADUM3473 function properly by supplying either the VDD2 pin or Vreg pin with regulated 15 volts from the downstream 15 volt LDO supplied by the 16 volt Viso output?  Which would be preferable, supplying the VDD2 directly or just the Vreg pin? Can the Vreg pin be left floating if unused?

Thanks for your help.