Earthlink tops out at 768 i believe, so I wouldn't go with them. However, if you're too far from your local phone center there might not be anything you can do for faster DSL. You might check into cable broadband if you already have cable. If not you're going to be spending a lot more per month. Good luck!
You have 1.5 though? I think you might be too far from the phone center to qualify for 3.0 then. Sure 3.0 is nice, but 1.5 isn't too shabby. However 768k is becoming the new dialup.