172.16.15.38 lies in rfc1918 address space it wouldn't be routable on the internet.
Click on the spanner under gateways and display both, guessing you have a "Rogue" monitor IP thats got in there somewhere, delete it if it shows.
Also check System -> Routing -> Gateways -> Edit
Thinking about it, maybe someone has configured 172.16.15.38 on the OpenReach VDSL modem and pfSense has piclked up on it, you can get stats off some of them.