You get two things with your hosting, disk space to put your files on for a website and access bandwidth. The thing that concerns me about 15000 mb of bandwidth is that they might be overselling their product and therefore increasing the access times (this is what people refer to when they ping something on a website like your domain), which means that access to your web browsing gets slower. I'm not saying this is the case, but it has been mentioned to me from people I trust in the industry that people oversell their hosting products, banking on the fact that people won't use it all up every month if at all.
I have 550meg and 8000meg as my hosting package and never use anywhere near that. I have thought about surpass hosting, but recently I have asked two pre sales questions, the first question too 72 hours to answer and the next question took a month to answer. The reasoning behind the delay was they were busy. That is something that worries me with hosting companies. Not being able to get tech support with in a few hours and taking too long to fix, repair, reboot, relay information quicking is the main issue with hosting companies.
I was looking at changing to them, to increase my disk space and bandwidth for essentially the same price I pay currently.
I would ask surpass hosting how many packages they sell per webserver (hardware) they have.
My bandwidth at present for all my websites is less than 10meg a month and that is with about 700-1000 spam emails a month as well. Getting sick and tired of all the medication emails to help me with the wife, it is just crazy.
I hope that helps you with your hosting.
If you are setting up packages it is a good idea to consider what the disk space requirement they would need and allocate bandwidth according to how many packages you could totally setup. So say you set up 10 packages then you would allocate 200meg disk space and 3000meg of traffic bandwidth per package or even half of that and get 20 packages of 100 and 1500, which ever works. I personally setup from 10 meg to 200 meg and 100 - 1000 bandwidth for my packages that I sell, and adjust someones needs accordingly which takes all of 10 seconds to adjust.