As an early poster said, it depends on your physiology. The atmospheric pressure (and hence available oxygen) is about 13 percent less at 5000ft than at 1500. If you are O2 limited (you have to slow down on uphills cuz you're huffing and puffing so bad) at 1500, 5000 feet may further limit your speed/ability to climb, etc. If you are muscle or heart limited, you may not even notice a difference.