You're under 15s in the effort pace ... pretty darned hard to get under 15s on anything but smooth road. You need a watch! Wait for your birthday and maybe one will show up, or I think I would recommend a Forerunner 25 for you. Simple, but pretty good battery life (10 hours), same as mine.
Or the mega Forerunner 920XT for FORTY hours of "Ultra" battery:
Gosh, maybe I
should get one of those. ;) Maybe a present for myself if I meet my 1200 miles before Aug 13th goal.
See how I turned that into "about me"? :)