As you have already had 12 months with a partner-sponsored visa, the next one can only be for 12 months (so you will have had a total of 24 months). INZ expect couples continuing to live together to get a partner-sponsored residence visa to carry on after 24 months on temporary visas.
Of course, as you've been together for at least 12 months, you WOULD already be eligible to apply for partner-sponsored residence. It would be a good idea to keep careful copies of all the evidence you are submitting with this application, because you can use it also for residence. As there are such bad delays for a lot of people, you may want to apply for residence as soon as you can manage, so you are not waiting for the visa to come through when this temporary one is about to run out.