"Floating" x-axis in plot (animatedline)

I want to display a signal that changes over time, see the following minimal working example:

figure
curve = animatedline;
grid on;

stop = false;
startTime = datetime('now');

while ~stop
  signal = rand();
  t = datetime('now') - startTime;
  addpoints(curve,datenum(datetime('now')),signal);
  ax.XLim = datenum([datetime('now')-seconds(15) datetime('now')]);
  ax.YLim = [0 5];
  datetick('x','keeplimits')
  drawnow
end

I want to continuously display the last 15 seconds of date. Data older than 15 seconds should not be displayed anymore. However, the diagram currently visualizes the overall amount of data. Where is the mistake in my code / How can I achieve the desired behavior?