There two types of tracks
Routes and courses
Routes have lots of points and you can't use map mode because fenix will try two find a solution for each point and that take a lot of time. You have to use…
If you have created a track, you don't have to set it to 'Use Map', just set it to 'Follow Course'. If you send it to the device using the Connect Mobile app, instead of placing it in the NewFiles folder, the app will add waypoints with TBT directions. This way you can start immediately, no more 'calculating...'
If you have planned the track using on your computer, and downloaded the GPX files on it, you can send it to Connect Mobile in several ways, e.g. by emailing it to yourself. A decent route planning site also works well on mobile, so you can create the route on your computer, then open the site on your mobile and download the GPX. It should be opened by Connect Mobile.