If you think it's obviously too difficult for you right now, I think you should still keep this one on your practice schedule, but not as your main focus. Pick some pieces that are level 6 or 7, work on them. While you do that, sight read the level 8 one, get familiar with it, practice it couple times a week, but that's it. I think if you put too much effort on something that's too time consuming, it's a waste of time, because in the long run, when your ability improves, you'll definitely be able to play it much more efficiently (time wise and skill wise.) Be sure to tell your teacher that, otherwise, he/she might pressure you on learning it when you can take that same amount of time learning pieces that are more difficult, but obtainable to you.You need effort and set practical goals when it comes to learning piano. Well, can't cheat your way through piano, can you?... like I did through high school.