There are reports of VA spot-checking carry-on baggage to check for the 7kg limit. This is not a comprehensive thing (I've never seen it), but it is possible. Other airlines like jetstar will weigh every carry-on. Virgin will not. So if your carry-on doesn't look heavy, you might be OK.
Also consider that the 7kg limit does not include a personal item, which can be a laptop, so if you have a heavy laptop that is OK.
https://www.virginaustralia.com/au/e...ry-on-baggage/
As for checked baggage, I have checked a 54 linear in bag before and never had it measured. Once they asked me if it was oversize, and I said no, and that was it. Not sure how much bigger your luggage is (the 54 in bag is something I carry for work, never on God's great earth would I choose to travel with anything that size, let alone bigger!).
The VA website says oversize bags may travel as long as they don't exceed 32kg, but to contact them before travel. Not sure what that means, but you may be able to take your big bag with a fee.