subscription slow in RN, but not on web app

OK, bear with me; I am retrieving a collection of 10,000 docs, which I realize is a lot, but I'm trying to see if I can get it to work acceptably.

In the web interface, my subscription loads and is ready in 2-12 seconds, depending when I start counting (page load or subscription start/end time, page load being relevant because SSR passes the initial docs). This is acceptable.

On the mobile device, subscriptions take 30-70 seconds, which is obviously way too long.

Any ideas what might be causing this, or where to look? Some notes:
- I initially thought it was the offline package I've been working on, but that actually speeds it up (it inserts cached docs to minimongo, which presumably then difs and merges skipping some docs).
- I also practically ruled out the DOM, as for my test I just have a Text component listing the subscription status.
- Possibly related to this issue, but it seems like it shouldn't be taking this long anyway: https://github.com/meteor/meteor/issues/7649