You should have no trouble running 10-15 km as a training run. Your training track should include some forest terrain and ascending slopes. If, in addition to that, you are also capable of including short sprints, speed-increase runs and intervals, you should be fit to participate.
The actual challenge of TOUGHRUN lies with your personal toughness and local weather conditions. Be prepared to get wet very early on and that that will not change until after the run. Depending on the weather and temperature, some thermal wear may be in order. We do advise against neoprene suits, however. Synthetic fibres or fast-drying thermal underwear is usually the way to go.