Where to LFG past lvl 15?Follow

I grouped in Blackburrow and Antonica between 10 and 20 (you can do the spiders in BB around 18 or so). I also did Stormhold, which is good till you're in your mid 20's.

After 20, try to get a group in the Thundering Steppes, then around 25 or 26, move to Varsoon's or keep going in TS.

If you're on the Freeport side, then I'm not sure what to tell you.

After wailing caves greys out to you, go explore the rest of the commonlands. Go kill dervs, there are some quests for them around so you should be able to find a group. Also, take the griffon to the ruins and hunt there, certainly some good xp for ya there in a group. Get your FG quest soon and start that which will lead you to giants which are also good xp for your lvl.