We need to have a reason to care about your story or your characters in order to become invested. Talking scenes aren't automatically boring, but you can't walk up to a random person and start telling them your life story and expect them to care -- and it's no different if the person telling the life story is fictional! We have to have met them and come to care about them before we'll be interested in all that.
You say it's like a TV series instead of a movie, and that's fine -- but if you tune into a TV show for two weeks and you still don't know what the story's really about or why you should be watching, you're not gonna tune in again.
Why do you feel like your story needs that slow start? Why does it need that exposition in the beginning? I mean this as a genuine question -- do you have an answer for why the story is better that way, and why that build-up is needed?
You talk about flashing forward to some action -- imo that might be a red flag that you're using the idea of a flash-forward as a crutch for a boring opening, basically the equivalent of saying "I promise this gets interesting later!!" It's... I mean, you CAN do that, but if that's the case, it'd be way better to actually make the beginning of the story not boring!
So what scene would you flash-forward to? What's the first REALLY INTERESTING part of your story? And follow-up question: why can't you make that the opening scene -- what information would we be missing? Anna's advice is some I've heard too, phrased as: "start as late in the story as you possibly can" -- think about what would happen if you cut out as much of the beginning as you can, and see how much of it is really necessary to the story!
THAT SAID, please don't make the mistake of thinking action = interesting, not-action = boring. Over the Garden Wall is a 10-episode cartoon series that is unsettling and funny and excellent storytelling, and yet 90% of the show is walking and talking. It contains TONS of exposition, but you don't notice that -- you don't register it as exposition -- because the characters are engaging and fun, and so opening on these two kids just talking about how they're lost and talking to a magical bird about whether not or not she can get them home and talking to the woodsman about The Beast and debating with each other about whether or not the woodsman is going to kill them -- all of that is entertaining.
So when you say "it has a really slow start with lots of exposition," does that mean, there's talking, and we don't get to ACTION right away? Or does that mean, someone just telling us a bunch of information or explaining the world or the characters to us? Because the first one can be just fine, but that second one usually isn't. It feels counterintuitive, but it's often better to let that information come out AFTER we have a reason to care about it, later on in the story.