Sadly no.
To be eligible under UoA graduate entry scheme, you need to have completed or be completing a bachelor's degree, postgraduate degree (PhD or masters, or honors) or postgraduate diploma from a New Zealand university.
Simply put, a graduate diploma does not fall into either of those categories and therefore make you not eligible under the graduate pathway.
Even if it is a eligible degree, the timeframe for the degree is not in the minimum academic time. Normally, a graduate diploma takes 1 year of full time study to complete, taking 1.5 years would mean that you did not complete this in the minimum academic time.