Fantasie Impromptu is much more dificult than Nocturnes op 9... I dont know your level, I think Fantasie Impromptu must be level 8 or 8+. And, in the beggining, right hand plays 4/4 and left hand 3/4 wich isnt easy... So, if you arent level 8 yet, it will be better for you to wait a little. But only you know what`s your level

Best wishes
Rui