It seems I have mixed two issues here. The first one being the android project not building with Xamarin.Android.Support libraries version 23.0.1. For this you need to install the latest bits from Xamarin and to update your project to compile using Android API Level 23. While this has not been extensively tested, you should not expect issues with the current version or UI for Xamarin. It seems you have already done this.
The second problem is the java.lang.OutOfMemoryError thrown when building the Android project. While we're unsure exactly what has changed, this happens only when building with Xamarin.Android.Support libraries v 23.0.1. In this case you have taken the correct approach -- increase the max java heap size.
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