It sounds like a lot but it’s roughly the same weight in banana peels and sugar, it’s typical for this sort of jam. For reference: you could sub the peels for the same weight in strawberries, and the recipe still works.
EDIT: it is by no means something healthy to eat in large quantities. It’s a caloric bomb, just like any jam. But it works great as a bread spread, the banana peels won’t go to waste, and it packs a lot of potassium too. (Most potassium from bananas is in the peel, not in the flesh.)
I also have a banana cake recipe if anyone is interested. It uses the whole banana but you can tweak it to use just the peels.