You can also manually adjust the Area Battle level. This should help speed things up a bit until you reach the point where enemies start taking several minutes to defeat.
A quick reminder, as some other users have mentioned: early on, try to make use of Leech or Health/s to keep yourself alive while farming higher levels. Eventually, once you reach the Qi or lower levels, the armor % becomes so high that you can simply get a stronger DPS weapon and mostly disregard the Leech/Health/s effects. At that point, just adjust the battle level to the highest level where you can still deal some damage and the enemies can still hit you for -1 damage.