To find what percent some number [tex]a[/tex] is of some number [tex]b[/tex] is, then use the formula:
[tex]\dfrac{a}{b} \cdot 100 \%[/tex]
Essentially, find what proportion of the original number the new number is and convert it to a percentage.
In this case, [tex]a = 15[/tex] and [tex]b = 60[/tex], meaning that the percentage would be:
[tex]\dfrac{15}{60} \cdot 100 \% = 25 \%[/tex]
Our answer is 25%.