Havn't even beat any of the 3 first arenas that you only need to get to round 5 in, why? because no one will ever play with me, i actually made it to round 4 in 30 minutes but then ended up died, cried a little inside.
 I'm level 18 also. Add "Vile Slacker" if you want to play with me, I'm online right now if you read this, otherwise add me and we can do it tomorrow. 
I'm not gonna even bother soloing it anymore.
EDITTT:
Many People have added me and I thank you, the giantbomb community, I knew I could count on you :)

Honestly, Unless you have a maxed out character (or at least around lvl 50) and don't do the co-op split screen hosting with a level 1 character, these get incredibly tough. Especially the larger one's that If I remember take 2-3 hours a piece.