15 mile trail run

I am training for a spring marathon and a late summer 50 miler. My current long run is 12 miles and I have found a 15 mile trail run that is 2 weeks away. If I use the run/walk method ( that is how I train) and take it easy, would it be feasible to do this 15 miler? Would like to use it to get some experience with gear, nutrition etc...

I think you should be fine. Just run a smart race and know your limits, and start to taper your training before the race.

Good luck and have fun.
Greg

Feasible? Certainly. Just remember that you'll use different muscles (or rather use your muscles differently) on trails as opposed to roads and base your pace on perceived effort, not minutes-per-mile. It should be a good experience for you.