That is only 5 mph which is a little faster then walking. You should be able to go 10 miles in less then a hour. You want to keep working at it to get faster. Do an easy 10 min warm up ride and then start to pedal at a high cadence 70-90 rpm's with a lite pressure on the pedals. You want a gear that will get your breathing to the point where you can still talk but not sing. Stay in that zone as long as you can. If you need to catch your breath or your legs start to hurt drop down a gear or two and keep going. Ride for distance, you will get faster as you get stronger.
