Answer
For the same change in speed, the KE would change more if the speed was higher to start with.
Work Step by Step
KE depends on the square of the speed.
We see that $(30 \frac{km}{h})^{2} - (20 \frac{km}{h})^{2}$ is greater than $(20 \frac{km}{h})^{2} - (10 \frac{km}{h})^{2}$.