batchmode assetbundles slow across various ec2 instances

I have been playing around with creating assetbundles via Unity's (4.6.1f1) Editor command-line batchmode feature on various ec2 instances and was surprised to find that there was little difference in build time/performance from a simple t2.micro to much more powerful c4.large and even r3.large instances. My test case was a 2048x2048 jpg and it takes around 45 seconds regardless of the instance. Perhaps this may NOT be a Unity quesiton but curious how Unity's Editor utilizes resources of the server it is installed on.

The main bottle-neck (see below) seems to be setting TextureFormat to AutoCompressed. I know this might be slow on less stout machine but to see almost no performance benefit on an r3.large instance I just don't understand.

case: 2048x2048 jpg (1800kb) --> AutomaticCompressed

 void OnPreprocessTexture()
 {
     TextureImporter importer = (TextureImporter)assetImporter;

     importer.textureType = TextureImporterType.Advanced;
     importer.maxTextureSize = 2048;
     importer.mipmapEnabled = false;
     importer.isReadable = false;
     importer.filterMode = FilterMode.Bilinear;
     importer.textureFormat = TextureImporterFormat.AutomaticCompressed
     importer.anisoLevel = 1;
     importer.wrapMode = TextureWrapMode.Clamp;
 }