I with the help of a previous answer on here Different tocdepth for main toc and in-section toc, I have made it so my titletoc is able to contain subsections while my main toc does not have them. However, I noticed that the formatting for the titletoc toc has different spacing.
If I had set the main toc format myself, I would copy the parameters to mimic them for the titletoc toc. But since it is the default memoir format, I'm not sure how to replicate it.
Here is a MWE
\documentclass{memoir}
\setlength{\parskip}{12pt plus2pt}
\def\baselinestretch{1.6}
\linespread{1.3}
\usepackage{titletoc}
\usepackage{lipsum}
\setpnumwidth{2.5em}
\setrmarg{3.5em}
\begin{document}
\tableofcontents*
\setsecnumdepth{subsection}
\maxsecnumdepth{subsection}
\settocdepth{subsection}
\chapter{Chap1}
\section{Chap1Sec1}
\section{Chap1Sec2}
\chapter{Chap2}
\section{Chap2Sec1}
\section{Chap2Sec2}
\subsection{Chap2Sec2Subsec1}
\chapter{Chap3}
\settocdepth{section}
\renewcommand{\thesection}{\thechapter-\Roman{section}}
\renewcommand{\thesubsection}{\thechapter-\Roman{section}.\arabic{subsection}}
\renewcommand{\thepage}{S-\arabic{page}}
\section{Chap3Sec1}
\clearpage
\section{Chap3Sec2}
\startcontents
\printcontents{}{2}{\addtocontents{ptc}{\setcounter{tocdepth}{2}}}
\lipsum[1-2]
\subsection{Chap3Sec2Subsec1}\clearpage
\subsection{Chap3Sec2Subsec2}\clearpage
\subsection{Chap3Sec2Subsec3}\lipsum[1]
\subsection{Chap3Sec2Subsec4}
\stopcontents
\section{Chap3Sec3}\clearpage
\section{Chap3Sec4}\clearpage
\section{Chap3Sec5}\clearpage
\section{Chap3Sec6}\clearpage
\section{Chap3Sec7}\clearpage
\renewcommand{\thepage}{A-\arabic{page}}
\setcounter{page}{9}
\chapter{Chap4}
\settocdepth{subsection}
\section{Chap4Sec1}\clearpage
\section{Chap4Sec2}\clearpage
\subsection{Chap4Sec2Subsec1}
\end{document}
Here is a 2nd MWE showing the suggestion by lockstep, and now the new spacing issue. It uses the DoubleSpacing and SingleSpacing use as well from the memoir package
\documentclass{memoir}
\setlength{\parskip}{12pt plus2pt}
\def\baselinestretch{1.6}
\linespread{1.3}
\usepackage{titletoc}
\usepackage{lipsum}
\setpnumwidth{2.5em}
\setrmarg{3.5em}
\begin{document}
\addtocontents{toc}{\protect\setlength{\parskip}{0pt}}
\frontmatter
\tableofcontents*
\setsecnumdepth{subsection}
\maxsecnumdepth{subsection}
\settocdepth{subsection}
\mainmatter
\DoubleSpacing
\chapter{Chap1}
\section{Chap1Sec1}
\section{Chap1Sec2}
\chapter{Chap2}
\section{Chap2Sec1}
\section{Chap2Sec2}
\subsection{Chap2Sec2Subsec1}
\SingleSpacing
\chapter{Chap3}
\settocdepth{section}
\renewcommand{\thesection}{\thechapter-\Roman{section}}
\renewcommand{\thesubsection}{\thechapter-\Roman{section}.\arabic{subsection}}
\renewcommand{\thepage}{S-\arabic{page}}
\section{Chap3Sec1}
\clearpage
\section{Chap3Sec2}
\bigskip
\startcontents
\printcontents{}{2}{\addtocontents{ptc}{\setcounter{tocdepth}{2}}}
\lipsum[1-2]
\subsection{Chap3Sec2Subsec1}\clearpage
\subsection{Chap3Sec2Subsec2}\clearpage
\subsection{Chap3Sec2Subsec3}\lipsum[1]
\subsection{Chap3Sec2Subsec4}
\stopcontents
\section{Chap3Sec3}\clearpage
\section{Chap3Sec4}\clearpage
\section{Chap3Sec5}\clearpage
\section{Chap3Sec6}\clearpage
\section{Chap3Sec7}\clearpage
\renewcommand{\thepage}{A-\arabic{page}}
\setcounter{page}{9}
\chapter{Chap4}
\settocdepth{subsection}
\section{Chap4Sec1}\clearpage
\section{Chap4Sec2}\clearpage
\subsection{Chap4Sec2Subsec1}
\end{document}