Reduce Xamarin.Forms app size, remove support library v4?

Hi,
we're trying to make the most basic Android App using Xamarin forms. We use a couple of third party components (SignaturePad, Microsoft HTTP), and just a few xaml views.
The size of the compiled APK is 9,900 KB (release mode, linking SDK assemblies), which is huge for this kind of application. I've noticed a 2,200KB android support library v4, which is totally useless as we target android 4.4 up, isn't there a way to remove this DLL? It's unfortunately a dependency of Xamarin.Forms package.
Is there anything else we can do, or 10 MB is the minimum size of an app using Xamarin.Forms?

Thanks
Marco