The curve is kinda steep due to low amount of areas to build up towards. Perhaps They should put a level block on areas so people can't enter with out having at least 1 moga of that level on your team.
Either way, its just saying you need to level up, it only takes about an hour to go up one level arund level 20. and don't fight things your level, you'll waste to much attack. USE YOUR WHISTLES thats a free attack right there and you get to attack. Also fight monster 5 levels below you.