Howdy @Amelie_Str and welcome to the community! 
This is a fairly common issue that I’ve seen on a number of times around here (here, here, and here are some threads for reference) and the short answer is that there’s not much you can do to compress long Lottie image sequences outside of compressing the quality into oblivion — and even then these tend to be larger than what you’d want to use on most projects.
While Lottie is a super awesome library for adding motion to the web, but in reality they work best with vector animations and really should only be used with very short image sequences.
The suggestion I always recommend is the same solution folks like Apple use for their marketing pages which is scrubbing through a video file instead. The link below is what I reference in those threads which gives you an idea of some solutions:
It’s getting a bit old now (going on 3 years) so I’d imagine there are some other options out there, but hopefully that points you in the right direction. Good luck with the project! 