Level 1-7, and 2-6, are pretty good to farm for carrots.
Level 1-7 Average time of 1:30.
Level 2-6 Average time of 1:00.
Though 2-6 is much harder of the two.

A High Damage weapon is needed, and you need to make use of Dash attacks. Stamina booster is nice to use, while the carrot magnet will save a small bit of time. carrot booster don't work, so there no need. Killing the Boss will always drop about 500, and 500 from the chest they drop.