Your Jump check is modified by your speed. If your speed is 30 feet then no modifier based on speed applies to the check. If your speed is less than 30 feet, you take a -6 penalty for every 10 feet of speed less than 30 feet. If your speed is greater than 30 feet, you gain a +4 bonus for every 10 feet beyond 30 feet.
All Jump DCs given here assume that you get a running start, which requires that you move at least 20 feet in a straight line before attempting the jump. If you do not get a running start, the DC for the jump is doubled.
so for yer jump with running would put you at a 26, without would be 46 (figgure the distance DC then added the speed penalty)
but on a bonus note, if you make a 21 you can still make it with a dc 15 reflex then a dc 15 climb check