You can keep adding people until you hit a limit, but I'd think it like BFV, where 56-128k up AND down per person is good.
You can force people to use lower amounts of bandwidth with the following command in teh server files:
game.serverMaxAllowedConnectionType CTModem56Kbps
change CTModem56Kbps to CTCable128Kbps if you need more bandwidth per player
56k is enough to play okay... infantry is good, but vehicles are a bit choppy for the players. Setting more than 128k is not really necessary.
You can calcualte pretty well your number of players when using these different server modes, figure in at least 10% overhead.
I don't know if a T1 is 1500 Up/down shared, or if it's dedicated 1500 up and 1500 down
1500k shared up / down connection * 0.9 / 112k = 12 players
1500k up / 1500k down * 0.9 / 56k = 24 players