I think it would depend on what is causing the delay whether this constitutes a major failure or not. The following are only my opinions and are not to be taken as law. The ACL rights however are law and can be considered correct.
If the device was mishandled by you or others you allowed to use it or by software/apps you installed then you will not be covered by ACL.
As the device was purchased brand new this year (even up to around 2 or 3 years after purchase it could still be considered covered under ACL) if the fault is not of your making then
if it is a hardware failure then it is most likely a major problem,
if it is a software/firmware issue that can be remedied by reinstalling the operating software/firmware they may be able to argue it is a minor problem where they get the choice to refund, repair or replace.
As @TheBBG advises the backing up your data first & then carrying out a “factory reset” of your phone would be a very good step to take just in case a faulty update or a app has caused the problem. If the problem persists after a reset (or if you have already undertaken a reset & the problem still is occurring) then you will have to send to Kogan or their authorised repair place to have the device checked. When returning the device ensure you have removed all personal data, SIM/SIMs, and if installed your Micro SD card from the phone and send by registered post or by courier with a request of proof of delivery and insurance. These costs if reasonable & the device is found to be faulty as long as the fault is not due to misuse are able to be reimbursed to you as part of your ACL rights.