Was looking for the cheapest way to renew my Office Microsoft 365 subscription, and found this at Bing Lee. For some reason they're charging the same for 15 months as they are for 12.
Works out to be the cheapest per month from what I can see, and I haven't seen the 15 month option anywhere else in Australia. I imagine if you do the enable auto-renew and turn it off you can make it 16 months.