Two sectors on one ticket does not automatically guarantee a connection.
However, I think 2.5 hours is ample for this transfer, although one or more of these factors may contribute to slower progress:
- late arrival of the inbound flight
- congestion in arrivals
- what you have in your luggage
If you have an ePassport/biometric passport (with a chip), you can use one of the SmartGates on arrival in Brisbane to avoid engagement with the odiously-named Border Force officials at immigration. (NZ also has SmartGates, which are smarter than the ones in AU because they have only one stage of processing, so you can get some practice with them there.)
On the other hand, if the queues on the SmartGates are long (it takes about one minute for each person to pass, so do the calculation), you may be better off using a gate staffed by an odiously-named official.
Depending on what you have in your luggage, you may have to submit to further examination. Foodstuffs, plant matter, wooden carvings, and dirty hiking gear, among other things, can all be problematic.
The link provided by #2 is on the right track, but this is a better page. Look under 'transfer information':
