What is left?

When 15 is divided by 16,the remainder is -1.

therefore when 15^300 is divided by 16,the remainder is (-1)^300=1

therefore the remainder when 15^300 is divided by 16 is 1

Here 15 and 16 are relatively prime. So by Fermat's Theorem $15^{15}$ leaves a remainder $1$ when divided by 16. So $15^{300}$ leaves the same remainder $1$ when divided by 16.

Applying the python Theorem, (15**300)%16