How much weight does this large animal need to put on to hibernate?

Hello there.

I have a strange but interesting question Id like to have answered that I cant seem to find answers for elsewhere.

I'm working on making a zoology book on an imaginary creature of mine

and Im trying to make it scientifically accurate as possible.

my creature is a 20 ft monster which weighs 15 tons. it is a hairless land mammal.
It is covered in thick blubber and has strong muscles powering and supporting its body structure.

the question I would like to know, is how much weight would this animal need to put on in order to hibernate for 5 months?

please let me know!

Alana V.