You're only two weeks into this. Don't even look at your speed yet. Add 5 miles to your rides this week (15 per ride, in other words). Next week add five more. The following week your average rides should be 25 miles, with a longer ride of up to 40 somewhere in there. Next find a good hilly area to work out in, and ride 20-30 miles. When ten miles becomes your warm-up segment, you'll be on your way toward building speed.

Check the net or your LBS for a casual group ride. Riding with others will help you monitor your progress. Numbers, averages, etc..... meaningless unless you're comparing the same ride with the same wind conditions, etc.