According to the Princeton Review, a score of 15 or lower on the ACT is consider too low for most four-year colleges. The highest possible score to achieve on the ACT is a 36.
A good or bad ACT score depends on the college a student wishes to attend. For some colleges, an ACT score of 23 is sufficient, but for others, a higher score may be required. Some colleges accept a low ACT score of around 15 as long has the student has exceptional grades and a high-quality application; however, the student may be required to take remedial courses to compensate for the low score.