Sustain Pedal Positioning

[Gilles]

Hello.

The default position of the sustain markings makes it clash
with the dynamics markings.
Unfortunately, I cant't seem to move it down; I've used

  \override SustainPedalLineSpanner #'padding = #15.0

inside the \score, but whatever the number, the line doesn't
move.
What am I doing wrong?

Thanks,
Gilles