There would have to be more details on the courses. 1000 feet over 15 miles is easy. 3500 over 25 could be tough if it's a 12.5 up then 12.5 down. Some riders may never make it to the top of the climb.
If it's 3500 spread evenly over the 25 miles, that could add up to a consistent 4% grade (guessing). Not tough but a serious climb for those that don't frequent hills.