Plot doesn't care about axis setting

Question

I have a Pgfplot and for some reason it does not care about my y-axis settings... I have set ymax to 15 but for some reason it only goes up to ymax is 14 or something...

Can anyone explain why? And how I fix this?

Since my plot is based on coordinate data (and the complete source) exceeds the input limit of a question you can download the complete source here: http://pastebin.com/nwNwuFam

However I also noticed that this also occures when I don't set any coordinate data...

\documentclass{standalone}
\usepackage{graphics}
\usepackage{siunitx}
\usepackage{tikz}
\usepackage{pgfplots}
\usepgfplotslibrary{groupplots}
\pgfplotsset{compat=newest}
\pgfplotsset{plot coordinates/math parser=false}

\begin{document} 
\begin{tikzpicture}

\pgfplotsset{%
  width=4cm,
  height=4cm,
  scale only axis,
  every x tick label/.append style={font=\scriptsize\color{gray!80!black}},
  xmajorgrids,
  xminorgrids,
  every y tick label/.append style={font=\scriptsize\color{gray!80!black}},
  ymajorgrids,
  yminorgrids
}

\begin{axis}[%
xmin=0, xmax=0.015,
xlabel={Time [\si{\second}]},
ymin=-10, ymax=15,
ylabel={$x_i$},
scaled x ticks=base 10:2]

\addplot [
color=blue,
solid
]
coordinates{};

\addplot [
color=green!50!black,
solid
]
coordinates{};

\end{axis}

\end{tikzpicture}
\end{document}