To evaluate the expression \(-1.5p\) for \(p = -31\), substitute \(-31\) into the expression:
\[ -1.5p = -1.5 \times (-31) \]
Now, calculate the multiplication:
\[ -1.5 \times (-31) = 46.5 \]
Therefore, the value of the expression \(-1.5p\) when \(p = -31\) is
\[ \boxed{46.5} \]