Unfortunately this is all too common in larger apps. There was a thread not too long ago about reducing build time so you could start there. Disabling build-time linting can be a big help…
You could also try out Embroider, Ember’s next-gen build system which (at least eventually, possibly now) might be faster. It’s still under active development and some addons may still break with it but it could be worth a shot to try it out.