Ok Ok I got curious and looked myself…AU915 it is (as a standardised plan)
No one on the forum is likely to have the legal and regulatory knowledge and authority to suggest/authorise anything other (though I stand to be corrected! 
) and we rely L-A for guidance. Also if going off piste wrt using an unauthorised plan you should also consider availability of devices and how to be managed and configured even if general width of band ok it may be there are specific sub-bands that are a problem in territory & cant be correctly set/ajusted for COTS products and set frequency plans - also TTN supports standardised frequency plans by region (following L-A) vs custom versions so may limit capability and move out of scope for the forum.
Obvious question is why do you/would you want to go off plan vs simly follow L-A (they will have done all the due dilligence and Reg authority checks/negociations for you)