I'm using Chrome Devtools's Heap Snapshot feature, which allows watching the size of objects on my website to measure where/if I need to reduce the size of my objects.

However, I'm looking at the size of an object, which is supposedly 15.5MB, but its parts are only 1.6MB, 1MB, and 0.8MB:

Here is the structure of this object for reference (BiMap just being two Records for either direction):

interface Mappings {
    classes: BiMap<string, string>
    noDescriptorToDescriptorMethods: BiMap<string, string>
    descriptorToDescriptorMethods: BiMap<string, string>
}

Unless my math is really rusty and 0.8 + 1 + 1.6 = 15.5, what is going on here?