Not really, i have seen one Person Level 19 the other are under Level 15. But it is right that we can better get Level ups, with exp boosts from quests and the start with Level 8 (beta reward) is this easy.
This is normal, if you got a group of real friends grinding with experience cash shop items, there will be easily level up in this game.. Just buy the cs experience and boost your grinding, there is already lvl 40s - 50s in the game which grinding around.. If you not willing to buy any then you can only spend your time slowly level up..
I'm not in a real rush to get to the high levels. Besides, this isn't the only game I play to pass the time. I've only made it up to 16 and I'm content with it.