The total length of the wall is 4.5 m, which is equivalent to 450 cm. The total length covered by the frog in one jump is $30-15=15$ cm.

To cover 420 cm, the number of jumps required is:

$420/15 =28$ jumps

In the 29th jump, the frog will reach the top of the wall and will not slide down.

Hence, the total number of jumps required is 29.