The degree of a quotient when dividing polynomials is given by:
\[
\text{Degree of Quotient} = \text{Degree of Dividend} - \text{Degree of Divisor}.
\]
Here, the degree of the dividend \( p(x) = x^4 + 2x^3 - 17x^2 - 4x + 30 \) is \( 4 \) and the degree of the divisor \( q(x) = x^2 + 2x - 15 \) is \( 2 \).
Thus, the degree of the quotient is:
\[
4 - 2 = 2.
\]
Therefore, the degree of the quotient is \( 2 \).