So I will give you my thoughts, just my personal opinion. I think if you really want to learn the Bénédiction de Dieu dans la solitude, then give it a shot. Based upon the repertoire you have listed (of I'm sure you have learned other pieces along the way), I would say you have a level of technique that should be able to handle this. Will it be hard? Sure. Will you have some gaps in technique? Sure. But you will learn these as you go. So I wouldn't worry about whether it would be too hard at this point. I think you can do it.
Obviously, you have a teacher and their opinion will be very valuable as they will have a better understanding of your abilities and other time commitments for other pieces, etc. I would definitely encourage you to bring up this piece as I personally find it to be one of the best that Liszt wrote. Their opinion would certainly be nice to hear. But, also, I have sometimes learned things (at your young age) that my teacher didn't approve of because I was so inspired by a piece. I only played it for her after I learned it, and she was pleased. However, I don't necessarily encourage this behavior, just trying to emphasize that your drive and interests can be huge factors in the equation of whether to learn something or not (within reason of course).
The piece is very long. I actually learned this piece myself during the pandemic and I would like to say it is such a joy to play and it is just so much fun. While I did have a number of more difficult pieces under my belt in comparison, I was just really driven to learn this piece. As an aside, I have found some pieces that should be easy for me to be a huge pain solely based upon my personal drive and interest in said piece. So my ultimate advice is to just give it a shot. If you really adore this piece, go for it!
For learning it, I actually split it into 3 sections (which are obvious when you listen to it). The first section being before the choral middle section and the last section starting with the running base and return to the theme of the first section. I tried to tackle some of each section at the same time. I personally found the first section of the piece to be the hardest for me to learn with all of the two-note chords throughout (like almost a slow trill with the top 2 notes and an arpeggio in the lower notes, which made it harder to sight-read initially for me) and had to make sure I wasn't keeping my hand stretched too far during this section. However, once I got it down, it became much easier to play and it feels so very fluid to me now. Just don't rush it.
With all of that, I think it is a good choice if you really like the piece. Unless you have another reason for learning something shorter, say for a particular repertoire, competition, audition, etc., then I would encourage something else.
I hope this helps. Also, I wouldn't say the liebestod is unrealistic for you either and is much shorter.
Best of luck with what you and your teacher decide. Let us know what you choose!
-KC