can i replace the isight of my 6plus under the isight replacement program here at nz even if i purchased it on USA?

Hi

Subject to the terms of the program, if the rear camera on your iPhone is producing blurry photos and falls within the eligible serial number range, Apple will replace the iSight camera for you, free of charge.

Follow the instructions here for your country:

https://www.apple.com/support/iphone6plus-isightcamera/

Note that the terms state that Apple may restrict or limit repair to the original country of purchase.

I'm afraid that no-one here can tell you what Apple will decide. You are not talking to Apple here - this is a user-based technical support community.