Updating the environment (Ionic CLI, app-scripts, Cordova) just makes sure there is no “cruft” hanging you down. Especially upgrading Ionic CLI will also give better ionic info output we can use to diagnose your problems.
If you do not want to upgrade Ionic (ionic-angular) itself I completely understand - but this will be the biggest lever you can use to improve the boot time. But as I wrote, start with the environment stuff first and stay with ionic-angular 2.2.0.