NZ$15/person still seems like a drop in the bucket out of a $3.2B budget, especially since it’s boosting the local economy rather than going out of the country.
It's a bit more than 2% of the annual budget. How much higher should it go? There are tons of other things that need funding - healthcare (NZ has single-payer), coast guard / military, industrial / agricultural policy, environmental protection, etc.
The whole thing is a bit more, but much of that is not going to social sciences at all and a lot of things which are lumped together are useful - economics is a social science, for example, and if you search for the EHB code on the most recent awardees you’ll see that it includes things like studies on autism or suicide which seem pretty useful to me.