A sound of about 15 MB is the smallest executable size with Delphi for iOS (in Release mode without debugging information). You can try disabling RTTI generation if you do not need it. But not with much hope.
It is much larger than ObjectiveC "native", but it inserts all the Delphi RTL and FireMonkey libraries to complete the entire rendering, so it is larger.
A " plain Objective Pascal " executable file using iOS built-in controls compiled with FPC should be smaller. Or when compiled with Oxygene for Cocoa ", it should be much smaller.
But do not look only at the size of the executable file, think about the memory used at runtime and the overall speed. You may need to compare it with the HTML5 apps built into PhoneGap. FireMonkey may be slower when rendering on the screen, but inline code with ARC memory processing should be more powerful than JavaScript.
Do not forget that your smartphone has a lot of memory now .;)
Unfortunately, it is not possible to share some code with external libraries (.so) in iOS, so you cannot use something like Delphi packages to reduce the size of the executable.
Of course, Apple has always done everything possible to get developers to use their own tools and language. Like Microsoft, especially for Windows 8. Delphi for iOS does not claim to be better than XCode + Objective-C, but should be cross-platform so that you can share as much code as possible with your server or Windows / Mac OSX applications: you cannot use your Objective-C code outside the Mac world ... but you can share your Delphi code between platforms, even if the user interface needs to be rewritten for mobile phones. That's why a fairer comparison would be with JavaScript / PhoneGap, MonoDroid / MonoTouch or AppCelerator .
Some data retrieved from StackOverflow:
One problem: AFAIK - the size limit for downloading 3G in the AppStore is about 20 MB.