I wouldn’t think so. If you use a nipple that’s too slow, typically what you see is frustration from the baby during feeds b/c the liquid won’t come through fast enough, and in the end, they either have to suck really hard o feed for a longer time, or they just don’t get in as much during a feed.
When you use a nipple flow that’s too fast, that’s when they might take in too much during a suck, and that can cause gulping, pulling off, gagging, “choking”, or a really upset baby in general. I suppose that taking in too much during a feed could worsen reflux. But I don’t see how being on a slow nipple would increase spitting up. Hopefully someone else will have some more experience/insight into this for you.