15mbs up and down should do you VERY nicely - at least to get started! Especially if that's unmetered!
If you have the bandwidth, next you need to prep the network. A little home router isn't going to cut it and will fail under load very quickly. I talk about this a bit a few posts above. I'm more then willing to help out if you need some network setup suggestions.

Also, that 15mbps will last you for a while but it takes less users then you might think to exceed that in a real-time game. Our latest round of ES4 load testing exceeded 100mbps easily. Just watch your utilization once you launch and know that if it takes off, you are going to need to get real hosting still.