There is no mention of taking a penalty to tumble for moving more than half your speed. Has that been intentionally removed?
Also, it's never been clear to me how the "+2 for each additional opponent avoided in one round" works with tumble. We've always played it that you roll a tumble check for each opponent, and it gets harder each time. If you're rolling past 3 people, you need to roll a 15, 17, and 19 to get past them. But I've always suspected you make one roll for all oponents at the highest number. Could that be clarified in Pathfinder?
Lastly, DC 15 + base attack bonus seems high for tumbling to me.
/ali