Sprite Packer Causes Unity to Hang on 5.5.0f3

Hi,

I'm working on a project with around 1500 different sprites, most about 500px by 500px in size, give or take. I'm getting some memory leaks on my iOS build, so I wanted to use the Sprite Packer to reduce the Draw Calls, and better use memory. Whenever I try to use the Sprite Packer, it gets about 399 sprites in, before the Unity application stops running on my Mac, and I have to force quit Unity.

Now here's the strange part: this seems to only happen when I'm on the iOS Platform. When I switch to the PC, Mac, Standalone platform, it packs the sprites fine. When I switch back to iOS, and it repacks when I go to make a build, Unity hangs again somewhere between sprite 336 and 399, randomly.

Has anyone else had any issues with Sprite Packer for iOS builds? Am I doing something incredibly wrong? I have attached an image with my settings on my sprites for reference.

Also I'm using: Unity 5.5.0f3 MacBook Pro (Retina, 13-inch, Early 2015) 16gig of RAM

Thanks!

Sean