Fitting tikzpicture in beamer: Difference between using \resizebox and \adjustbox?

Fitting tikzpicture in beamer: Difference between using \resizebox and \adjustbox?

  \documentclass[10pt]{beamer}
  \usepackage{amsmath}
  \usepackage{amssymb}
  \usepackage[english]{babel}
  \usepackage{color}
  \usepackage{float}
  \usepackage[T1]{fontenc}
  \usepackage[latin1]{inputenc}
  \usepackage{pgf}
  \usepackage{setspace}
  \usepackage{textcomp}
  \usepackage{tikz}
  \usepackage{verbatim}
  \usepackage{mathrsfs}
  \usetikzlibrary{arrows,shapes}
  \usepackage{adjustbox}
  \usepackage{pgf,tikz}

  \mode<presentation>{
    \usetheme{Warsaw}
    \usecolortheme{crane}
    \setbeamertemplate{navigation symbols}{}
    \setbeamercovered{transparent}
  }

  \title{Disks}

  \AtBeginSubsection[]{
    \begin{frame}<beamer>{Outline}
    \tableofcontents[currentsection,currentsubsection]
    \end{frame}
  }

  \begin{document}
  \begin{frame}{Initial solution}
  %\begin{adjustbox}{max size={.95\textwidth}{.8\textheight}}
  \resizebox{11.5cm}{!}{%
  \begin{tikzpicture}[line cap=round,line join=round,>=triangle 45,x=1cm,y=1cm]%, scale=0.5]
      \coordinate (b) at (13,3) ;
      \coordinate (c) at (14,3) ;
      \coordinate (d) at (15,3) ;
      \coordinate (i) at (9,5)  ;
      \coordinate (g) at (9,4)  ;
      \coordinate (e) at (9,3)  ;
      \coordinate (n) at (5,3)  ;
    \coordinate (o) at (4,3)  ;
      \coordinate (p) at (3,3)  ;
      \coordinate (a) at (12,3) ;
      \coordinate (m) at (6,3)  ;
      \coordinate (h) at (10,5) ;
      \coordinate (j) at (10,4) ;
      \coordinate (f) at (10,3) ;
      \draw (p) circle [radius = 3];
      \draw (d) circle [radius = 3];
  \end{tikzpicture}
      }%
  %\end{adjustbox}
  \end{frame}
  \end{document}
In the MWE above,
When I use \resizebox to scale the picture, the entire picture (2 disks) are visible, provided I do not exceed 11.5cm (a value found out by trial-and-error, something I want to avoid)
Hence, I tried using adjustbox (as mentioned in the question here), but if I used adjustbox by commenting the resizebox block and uncommenting the adjustbox line, the effect was as if I hadn't used it at all (the disk on the right was completely left out of the picture)  What am I doing wrong? I could finish my current slides using resizebox, but I wanted to use the "better" way of "scaling only if required" using adjustbox, and wanted to understand why it isn't happening in my case...