[Tex/LaTex] Reducing line spacing in chapter headings

chaptersline-spacingsectioning

I changed line spacing to double using \begin{doublespace}. Now for those chapter headings which are spread over two lines, I want to reduce their line spacing. How can I do that?
MWE

\documentclass[oneside,12pt,chapterprefix ]{scrbook}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage{graphicx}
\usepackage{enumerate}
\usepackage{setspace,xparse}
\usepackage{caption}
\usepackage{lipsum}
\let\oldchapter\chapter
\RenewDocumentCommand{\chapter}{s o m}{%
    \IfBooleanTF{#1}
    {% \chapter*
        \oldchapter*{\singlespacing #3}%
    }{% \chapter
        \IfValueTF{#2}
        {% \chapter[..]{...}
            \oldchapter[#2]{\singlespacing #3}%
        }{% \chapter{...}
            \oldchapter[#3]{\singlespacing #3}%
        }%
    }%
}
\title{Title of Thesis}

\date{2016}
\titlehead{A Thesis submitted for the degree of Doctor of Philosophy}
\publishers{}
\usepackage[left=1.50in,   footskip=0.4in ]{geometry}
\begin{document}
    \frontmatter
    \tableofcontents
%   \listoftables
%   \listoffigures
    \include{Abs}
\begin{doublespace}
\mainmatter
\include{chap1}
\include{chap2}
\end{doublespace}
\backmatter
\bibliographystyle{IEEEtran}
\bibliography{myBib}
\end{document}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%% Chapter 1 File
\chapter{A default chapter title}
\label{chap1}
\lipsum[1]

%% Chapter 2 File
\chapter{A lengthy chapter title that spans multiple lines}
\label{chap2}
\lipsum[1]

Best Answer

The following example updates \chapter and prepends it with \singlespacing so the entire heading is set without the doublespacing spread:

enter image description here

\documentclass{report}

\usepackage{setspace,xparse,lipsum}

\let\oldchapter\chapter
\RenewDocumentCommand{\chapter}{s o m}{{%
  \singlespacing
  \IfBooleanTF{#1}
  {% \chapter*
      \oldchapter*{#3}%
  }{% \chapter
    \IfValueTF{#2}
    {% \chapter[..]{...}
      \oldchapter[#2]{#3}%
    }{% \chapter{...}
      \oldchapter{#3}%
    }%
  }%
}}

\begin{document}

\doublespacing

%\tableofcontents

\chapter{A default chapter title}
\lipsum[1]

\chapter{A lengthy chapter title that spans multiple lines}
\lipsum[1]

\end{document}