Your no different than the people this normally works well for. Being in the "zone" for most people is a very pleasurable activity. If one could sit down or start running and immediately be there, procrastination would be a much smaller problem. It is precisely this unproductive, introductory stage that this method is compelling you to complete in order to get past. By forcing 15 or however many minutes a day you are hoping that more times than not this period will transition into one of productivity in which you don't need to time or force yourself to do more. Some days this won't happen and you can quit after 15 minutes. But for some it equate to more long term productivity sessions per week than strictly scheduling each long term session.