We hear you on the time commitment to reach level 15 (and that is where the elite costumes are). We want it to take you a while to get there, but not be unobtainable (because the costumes are cool, we want people to wear them!).
We set out to create a long progression curve with lots of leveling content, but we overshot a bit. So we are currently rebalancing the progression curve to lower the overall time requirement to reach level cap. Early levels, up to 4 or 5, will be essentially unchanged, and after that level progression will be steadier, with less of an extreme ramp up from level to level.
New level 15 will be about where level 13 is now, and those costumes will still be difficult to get, but within reach.
These changes should be coming soon.