What's the best way to use big textures (2048*1536) in Unity3d with NGUI on ios?

I'm using Unity3d (4.3.1) and NGUI for creating an 2d iOS (iPad) app. Also I need to use a lot of full screen images (about 100 images with size 2048x1536), for Gallery for example. Now I'm using them with GUI type, override for iPhone with max size 2048 and compression quality: normal. And I'm using a UITexture with Unlit/Transparent shader to show them. However, after about 40 images in the project XCode returns the terminated due to memory error. So the question is, what type of images do I need, and with which preferences to make them work? I'm using iPad 3 as a test device with XCode 5.1.1. I'll be thankful for any help!