Yeah, Decker can definitely chug a bit with larger file sizes. I don't think there's a hard limit necessarily, but there's definitely a practical limit. With my own work I'd ended up with an almost 200mb deck that REALLY chugged when you saved it and wouldn't even load properly in a web browser, so I had to downscale some of the assets, and then at around 60mb it would at least load in a browser.
I think the pertinent question would be, what are you doing that the file size is so big? I've noticed the bigger Decker decks tend to be from using a LOT of imported dithered art, and unless you're being silly like me and essentially doing FMV, often what tends to make the filesize balloon out like this is having multiple copies of the same card with slight differences, the problem being that each copy has to be saved in full in the deck. Could it be possible to rework things so that instead of different cards you're showing/hiding different widgets?