Your tanks are probably not swapping fast enough. Anything above four stacks is MURDER. We generally swap on the first add pack, then at 3-4 stacks, then on the next add pack, and so on. Keeps the tanks at or below 3 stacks at all times. Make sure that only one tank is standing in front at a time, since the stacks are refreshed by the cleave.
Healing this is definitely challenging. It is very important to CC the D-15 add in each spawn, then kill the healers, AoE the little guys, and finally kill the D-15. Having a Cunning class or a Sentinel/Marauder is really good for that, since their droid CC has no cooldown. Here's a video from a very-laggy commando healer's perspective. There were a few 20k+ hits on the tanks, but not many and we were mostly able to keep ahead of it. http://www.youtube.com/watch?v=NTwIamKuTXw
Note that we did actually have people getting caught in the field a few times. It was bad, but it's not really a wipe-inducing effect as long as your healers are on top of things.