Ah, I see. I should have noticed this before. Usually a balance with a stamp of 2440 is actually 25" long, not 15". If your balance channel is only 15" long, the stamp would be more like 1440. But the 1440 option can't support anywhere near 25.5 pounds.
You might want to double check just in case, since there isn't a 15" long channel that can support a 25.5 pound sash. It's a pretty heavy sash for such a short channel.