Final answer:
According to Chargaff's rule, in a DNA sample, the percentage of adenine is equal to the percentage of thymine, so if there is 15% thymine, there will also be 15% adenine.
Step-by-step explanation:
In the context of DNA base composition, Erwin Chargaff's rules show that the amount of adenine (A) is always equal to the amount of thymine (T), and the amount of guanine (G) is equal to the amount of cytosine (C). Given that in a DNA sample, 15% of the bases are thymine, we can apply Chargaff's rule which tells us that the percentage of adenine will be the same. Therefore, in this DNA sample, 15% of the bases are also adenine.