Only biking at 6mph...too slow?

It takes time to get faster. Read the other answers, there is some excellent information. Before you worry about speed, you have to work on extending the amount of time you spend on your bike. 10 minutes is not really even enough time to properly warm up. Warming up is accomplished by starting at an easy pace, allowing your heart rate to gradually increase as your muscles ready themselves for exercise. A good warm up will take about 15 minutes, after which you can start to push yourself harder