My app is 100M on Android, but it is more than 450M on iPhone. I am looking for a solution to this, but I heard buying pro version is the only solution. So I wonder how much pro reduce build size, generally.
Actually I am using a lot of images in the app. Should I buy pro to fix this? 
SInce Unity 5.x, there are no feature differences between Personal and Pro editions of Unity that will make any difference to build size. You’re probably talking about stripping options, which were a Pro-only feature in 4.x. However, it sounds much more likely that your problem is caused by your choice of texture compression option on the different platforms.
I recommend you go through your textures carefully with reference to http://docs.unity3d.com/Manual/class-TextureImporterIos.html
Well, i have a same problem about ios before. I don’t know about the pro, but i can reduced the app size by following this optimization. At least i can turn a 1 GB app to about 600MB. Ah, and for your information i don’t use unity ios pro for that.
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