Where did you get the B315 from?
That may be the issue, I know that the B315 that Vividwireless works, but if its outside of that then that may have had a different IMEI range then Optus has allowed.
IMEI is the unique identifier that provides detail to what hardware it is, Optus use this in the filtering for these devices.
Nowhere does it say the devices must be purchased directly through Optus or Vividwireless's retailers.
As for them adding it - not sure on that side, seems an uphill battle.