3 Mbps should be plenty. Most of raiding is dependent on your hardware, or not trying to push too high of a level of graphics. The actual internet connection really only plays a part in the in the Ping. Basically, how long it takes your Pc to communicate with the server. If you have a ping under 200ms, you'll be fine. Ideally, it'll be around 50ms.
How do I know my ping? I'm from the Philippines