I'm afraid it's a lot more than a couple of days. 14 days minimum, probably longer, possibly never. That's what Jeff meant by patience.
One way to hurry it up is to use the telnet interface of the DGN2200 to tweak the target noise margin even higher. This will reduce the connection speed still further, but the big advantage is that it will improve the stability and reduce the error rate. This will make DLM more inclined to reduce the target noise margin. After it does so, give it a few days to confirm that it's still stable, then you could remove the tweaking and get back your full speed.