全部はると規制されそうで
こんな感じです

ipv6 prefix 1 ra-prefix@lan2::/64
ip lan1 address 192.168.15.1/24
ipv6 lan1 address ra-prefix@lan2::1/64
ipv6 lan1 rtadv send 1 o_flag=on
ipv6 lan1 dhcp service server

dhcp service server
dhcp server rfc2131 compliant except remain-silent
dhcp scope 1 192.168.15.2-192.168.15.191/24
dns host lan1
dns service fallback on
dns server dhcp lan2
dns server select 500000 dhcp lan2 any .