The ideas about splitting the meals and seperating the dogs are both really worth a try. Some will respond to an area with fewer distractions well but others will just fret and ignore the food even more. You could try organised group feeding - I have used this many times with success (and many times with none, I have to say!) Get both dogs to sit while you put the food down, far enough from each other so that you can stand between them. On a signal (I use a whistle as this also encourages a good recall as the association with food is built up) the dogs begin to eat. When each finishes they are made to sit agin and must wait. You may find your slower dog will eat more when the pressure of the more dominant animal is taken away. (You may have to practice the sit until the signal for a few days first)

If this is not a viable option try splitting the faster dog's meal into two portions and the slower into three or possibly four. Feed the extra ones to the slower dog in another room. You can be sure they are both getting the appropriate amount and are reducing the amount the slower one has to face at each meal. This will also stimulate the dog's appetite and you may notice the need for smaller meals reducing over time.
I would also lift any food still remaining fifteen minutes after feeding - this will encourage the dog to eat a little quicker.
I hope this helps.