\- at the host open "Manage Virtual Networks" and adjust the IPs used for NAT to the 192.168.15.0/24 subnet (you have to modify the host-only range too since you use this subnet there already)
\- configure NAT networking for the guest
\- give the guest a static IP from this range (192.168.15.5)
\- define the default GW and DNS in the guest (the IP is 192.168.15.2)