The 6 1/4% discount is equivalent to a discount of 6.25/100 = 0.0625.
The amount of discount for paying within 15 days is 0.0625 x $6,439.65 = $402.48.
The 2.5% discount is equivalent to a discount of 2.5/100 = 0.025.
The amount of discount for paying within 30 days is 0.025 x $6,439.65 = $160.99.
The savings for paying within 15 days instead of 30 days is $160.99 - $402.48 = $-241.49.
Therefore, there is no savings for paying in 15 days instead of 30 days, but rather an additional cost of $241.49.