So I tested it on a simulator as well as as device and it is actually much faster now with CLI 3.10.3 even without updating the dependencies to the latest ionic, ionic-angular. The apk size is smaller and it loads much faster. But I am having some problems now. When I build with --prod the tab icons disappear and the push notifications do not show on the status bar anymore, they arrive (because I see them arriving on the icons badges if the App is opened) but if the app is in the background they stopped showing in the status bar.
I created a new topic here but no luck so far.