Ho, another one. Overall, as I checked the difficulty of the pieces I found that the Waltzes are a lot harder than the nocturnes you mentioned. The difficulty of the pieces are as follows:
Nocturne op 15 no 1: 8th grade
Nocturne op 37 no 2: 8th grade
Nocturne op 32 no 2: 8th grade
Waltz op 34 no 1: 8th grade
Waltz op42: 8+ or to be more specific, LRSM standard
Waltz op18: 8+ or LRSM standard.
JL