It really depends on the size of your level and the complexity of your meshes, both of which shouldn’t be an in your case (for iOS games). It will take 2x longer to build the lighting with a 2 core processor compared to a 4, but it shouldn’t be a big problem in your case again. I would personally get a quad core in your situation since a year from now who knows where mobile games will be at graphically, plan for the future I say. 