The transit bus from SYD domestic to SYD international terminals that VA uses, uses the main road, so even if you get onto the bus in the secure zone of SYD domestic, gate 45/46 downstairs, your bus will go out the main road, pick up poeple from outside the T2 SYD domestic terminal, go by the main road, to SYD intenrational terminal, and plonk you outside where every one is.
VA does not have online check in for international flights, so if you an get it, plea with the airport your domestic flight departs from, if they can some how get you an international boarding pass, even if on separate tickets. Also ask if they can onsend your baggage so you don't have to pick it up at SYD domestic.
2 hrs, especially if you have to line up at SYD international for showing passport for scanning, and getting a boarding pass, can take a while.
Ideally, I would have a more time between flights.
I have done the SYD domestic to international with VA and VA to NZ, but always on a linked ticket.
Try to get a link, if at all possible for your international VA flight at your domestic departure point.