Final answer:
The leading coefficient of the given polynomial is -15, which is determined after arranging the polynomial terms in descending order by their exponents.
Step-by-step explanation:
To find the leading coefficient of a polynomial, we look at the term with the highest exponent when the polynomial is written in standard form (descending order of exponents). Given the polynomial y = -10x^3 + 4x^2 - 15x^5 + 6x - 8, we should first rearrange the terms in descending order: y = -15x^5 - 10x^3 + 4x^2 + 6x - 8. In this form, it is clear that the term with the highest exponent is -15x^5.
Therefore, the leading coefficient of the polynomial is -15.