Once your cache is built it should only need to download new stuff. Unfortunately since it is a hog on resources you should clear your cache at least once a month so the old stuff is removed. Other than that a stable connection is important, not sure how fast it would need to be. And yes all platforms do the same thing. If you are getting stuck at 69% then your connection may not be strong enough.

If it is downloading each time then you are not downloading everything and it is trying again and again to complete its downloads. I suggest you find a time and place when you have a strong connection so that your downloads can complete. If you are not able to do this then either you need a stronger connection, a different device or you will need to give up on the game.