You likely would benefit from something faster to start. A good test would be how fast can you somewhat casually walk a mile? Lets estimate 16 min. Assuming you could wear a watch and knew where your mile marks were, you could beat the previous mile by just a few seconds with a slight change in pace at the end to get there in time.
Problem with starting at 30 min is if you took a whole minute off each mile, youd still end up wasting a couple hours before you got down to 15 min miles.
Biggest issue is not eating and drinking so finding the balance between going slow enough where you can easily ensure the continuously faster miles, and not wasting time while you have fuel.