Yes, it's actually possible. For instance, when you take the 15-day challenge, you can actually finish it in fewer days. Understand that 15 days is simply the average time that it will take a learner to effectively finish all the components laid out for each day. However, if your pace is faster then there's no need to wait. On the other hand, your pace might be slow, so you need to find a pace that perfectly suits your needs.