If you put the ZoneDirector and APs on untagged VLAN 15, leave the ZD System and AP Policies page configured with VLAN 1 (considered the untagged VLAN by Ruckus).
The ZoneDirector does not need to be a Trunk port, unless you tunnel any WLAN traffic.
The AP switch ports need to be configured as Trunk, with VLAN 15 untagged, and tag the additional VLANs required for your other SSID client traffic.
The client VLANs need DHCP servers, default-gateway routers, etc on those other VLAN sub-nets.
Assign the client VLAN from Advanced Options under your WLAN configuration.
I'm ex-Cisco, but translate the above to 3COM 5500 switch configuration.