Which version was this on? The latest APK seems to be leaner. That being said, Amethyst connects with 16 relays by default. If you and your followers have data in all of them, it will download 16 copies of everything. On top of that, many profiles pictures are quite big (10mb each). Since there is no rescaling of images yet, it's downloads everything it needs to render from the source, which can easily reach 2gb. Phones only reserve 250MB of local cache, which means once that limit passes, it erases old data to go get new one, redownloading some assets all the time.

That being said, i am using the latest APK v0.11.4 and it runs ok in 200k connections.