Answer:
No, you have to consider that if 1 student in 14/15 cannot represent a percentage between .69 and .71, how could 2 students do the job? You have to have an integer number of students.
2/18 = 1/14 = 7.14%
2/29 = 6.89%
Still out of bounds
What about 3 students?
3/42 = 1/14 = 7.14%
3/43 = 6.97%
3/44 = 6.81%
So, it looks like 43 is the minimum number of students.