Ahh - Remote Networks is not displayed for that sort of "Road Warrior" server, because that sort of server is not designed to be routing from the server out to some client "office" subnet. The wizard gives all the fields to type in, I don't think it has script to hide/display various fields depending on the type of server you have picked.\
That reachability should be just a matter of checking that all routers along the way know routes to/from all the various subnets, and that firewalls along the way are permitting packets to/from those subnets.
On pfSense OpenVPN server:
Local Networks - put something like 192.168.1.0/24,192.168.15.0/24,10.10.0.0/16
OpenVPN firewall rules - pass all that stuff (and more if that is then the way to the whole internet), and pass 10.15.0.0/16 as it comes back from Linux OpenVPN server.
Linux OpenVPN server:
Tell it that the pfSense client has 192.168.1.0/24,192.168.15.0/24,10.15.0.0/16 (whatever those networks are) reachable behind it.
Pass all the relevant networks.
traceroute/tracert should be your friend - use that to/from parts of the network and see where the traffic is hopping, and where it is not returning. That will give clues about which hop has router or firewall issues.