Well..
If you're level 21, you can either delevel back to 16 and delevel to level 7 skills, as davwtram said, or you could level to 24, delevel your skills to 15, get a nice sos or som level 24 bow, and sp farm where the little red box is on the map i posted here
The spawn rate is really good, especially in the middle, where a mixture of both chakji and devil/ghost bugs are. I levelled from 19-25 on this spot here really quickly on an old char, so you should be able to farm there pretty well.