This is a sincere response. It's pretty common for people to ask questions like yours and I do not understand why. I'm truly not trying to be snarky or anything. Can't you tell by working on a piece for a week or two whether it's something you can reasonably expect to handle or not? Why not just go for it? You love the piece. If you hit a wall, then you just put it aside and come back to it in a few months or a year or two. A teacher who's been working with you for a while may be slightly better able to predict whether you'll be able to handle it than you will, but even so, there's no harm in just working on it for a while and seeing how it goes.