removeShard() too slow

I have a MongoDB cluster with 9 nodes (3 shards, 3 nodes each). I’m now removing one shard, but the process itself is running extremely slow. Each node of the shard being deleted stores ~400Gb of data, which isn’t too much, I suppose. But approximation shows that the process of draining finishes in 200+ days.

I was wondering if there is a way to speed up this process. I have enough free resources (CPU, Mem, IO), I mean 3x more than nodes consume now. I’ve already looked at balancers settings like _secondaryThrottle or _waitForDelete without much success.