1) when i made server of another game, the upload that i have (8KB or 56Kb upload) was enough for 20 ppls easily, so i highly doubt that mir will need 100MB for 100 ppls top ^^
2) the server might be laggy for u for the reasons kaori sayed, and on the connection u have, and the connection the server have, and on the hour.
e.g if u play really late at night, or early in the morning, u will have no lagg if the server dont lagg no metter where u live, if u got lagg u can restart internet few times, and u will see diffrence in the lagg the game have, also try to shut down the music in the client option, and defrag the computer, it might give u less lagg.
3) try to shut down any programs that uses internet there (including keyloggers :P), and basicly any program u dont really need.