create vertical large table

Question

I am trying to create the following table, but it out of page bounds

\begin{sidewaystable}
\caption{My caption}
\label{my-label}
\centering
\begin{tabular}{|l*{16}{|c}|}
\hline
\multicolumn{1}{|l|}{\textbf{ }} & \multicolumn{5}{|l|}{\textbf{Benchmark}} & \multicolumn{5}{|l|}{\textbf{Graduate}} & \multicolumn{5}{|l|}{\textbf{Our Approach}} \\ \hline
\multicolumn{1}{|l|}{\textbf{metric}} & \textbf{Acc.} & \textbf{P. (FR)}& \textbf{P (NFR)}  & \textbf{R.(FR)} & \textbf {R. (FR) } & \textbf{Acc.} & \textbf{P. (FR)} & \textbf{P. (NFR)}  & \textbf{R.(FR)}  & \textbf{R. (FR) } & \textbf{Acc.} & \textbf{P. (FR)} & \textbf{P (NFR)}  & \textbf{R.(FR)}  & \textbf{R. (FR) }   \\ \hline
\multicolumn{1}{|l|}{\textbf{Case#1}} & 100% & 100% & 100% & 100% & 100% & 93% & 90% & 93.8% & 94% & 90% & 95% & 91% & 100% & 100% & 90% \ \hline
\multicolumn{1}{|l|}{\textbf{Case#2}} &  100% & 100% & 100% & 100% & 100% & 86% & 82% & 90% & 92% & 80% & 85% & 100% & 76% & 70% & 100% \ \hline
\multicolumn{1}{|l|}{\textbf{Case#3}} & 100% & 100% & 100%
& 100% & 100% & 91% & 93% & 88.6% & 88% & 94% & 90% & 88% & 81% & 80% & 90% \ \hline
\multicolumn{1}{|p{2cm}|}{\textbf{Average}} & 100% & 100% & 100% & 100% & 100% & 90% & 88.3% & 90.8% & 91.3% & 88% & 90% & 93% & 85.66% & 83.33% & 93.33% \ \hline
\end{tabular}
\end{sidewaystable}

Answer 1

To long for the comment.

Provided code fragment is not even close what is shown on image. Combinig bot the closet to what is on image is:

\documentclass{article}
\usepackage{geometry}
\usepackage{tabularx}
\newcolumntype{C}{>{\centering\arraybackslash}X}
\begin{document}
    \begin{table}
\begin{tabularx}{\linewidth}{|l | C|C|C|C | C|C|C|C|}
    \hline
    & \multicolumn{4}{|c|}{Benchmark}
        & \multicolumn{4}{|c|}{Graduate}                        \
    \cline{2-9}
%    & \multicolumn{4}{|c|}{Our Approach} &                     \ 
%    \cline{11-15}
    & \multicolumn{2}{|c|}{Accuracy}
            & \multicolumn{2}{|c|}{Precision (FR)} 
                    & \multicolumn{2}{|c|} {Precision (NFR)} 
                            & \multicolumn{2}{|c|}{Recall (FR)}  \ 
    \hline
1\textsuperscript{st} - party cookies
    & 29 & 17 & 27 & 20 & 93 &    &    &                        \ 
    \hline
1\textsuperscript{st}/3\textsuperscript{rd} party cookies
    & 19 & 22 & 23 & 20 & 84 &    &    &                        \ 
    \hline
Total
    & 48 & 39 & 50 & 40 &177 &    &    &                        \ 
    \hline
\end{tabularx}
\caption{Number of respondants for treatment}
    \end{table}
\end{document}

Please, edit your question and instead of code fragment provide a small but complete document, which can be compiled and which reproduce your problem (protrude out of page, if U understand you correctly.

Addendum: Finally you provide complete table code fragment. Unfortunately is still unknown page layout, which is essential for your table design. How much space is available for table? Who knows?

I assume, that page layout is determined by \usepackage[margin=25mm]{geometry}. If not, than you will hew new troubles ...

\documentclass{article}
\usepackage[margin=25mm]{geometry}
\usepackage[skip=1ex]{caption}
\usepackage{rotating}
\usepackage{tabularray}
\UseTblrLibrary{siunitx}
\begin{document}
    \begin{sidewaystable}
\caption{My caption}
\label{my-label}
    \sisetup{table-align-text-after=false}
\begin{tblr}{hlines, vlines,
             colspec = {Q[l, font=\small\bfseries] 
                        {5}{X[0.9,c,m, si={table-format=3.0{%}}]}
                        {5}{X[    c,m, si={table-format=3.1{%}}]}
                        *{5}{X[1.1,c,m, si={table-format=3.2{%}}]}},
             colsep  = 3pt,
            row{1,2} = {font=\small\bfseries},
             }
\SetCell[r=2]{c}

    &   \SetCell[c=5]{c}  {{{Benchmark}}} &   &   &   &

        &   \SetCell[c=5]{c}  {{{Graduate}}}  &   &   &   &

            &   \SetCell[c=5]{c}  {{{Our Approach}}}    &   &   &   &               \ 
metric

    & {{{Acc.}}} & {{{P. (FR)}}} & {{{P. (NFR)}}} & {{{R. (FR)}}} & {{{R. (FR)}}}
    & {{{Acc.}}} & {{{P. (FR)}}} & {{{P. (NFR)}}} & {{{R. (FR)}}} & {{{R. (FR)}}}
    & {{{Acc.}}} & {{{P.\ (FR)}}} & {{{P. (NFR)}}} & {{{R.\ (FR)}}} & {{{R.\ (FR)}}}   \
%
Case#1 & 100% & 100%     & 100%     & 100%     & 100% 
        &  93% &  90%     &  93.8%   &  94%     &  90% 
        &  95% &  91%     & 100%     & 100%     &  90%     \
Case#2 & 100% & 100%     & 100%     & 100%     & 100% 
        &  86% &  82%     &  90%     &  92%     &  80% 
        &  85% & 100%     &  76%     &  70%     & 100%     \
Case#3 & 100% & 100%     & 100%     & 100%     & 100% 
        &  91% &  93%     &  88.6%   &  88%     &  94% 
        &  90% &  88%     &  81%     &  80%     &  90%     \
Average & 100% & 100%     & 100%     & 100%     & 100% 
        &  90% &  88.3%   &  90.8%   &  91.3%   &  88% 
        &  90% &  93%     & 85.66%   &  83.33%  &  93.33%  \
\end{tblr}
    \end{sidewaystable} 
\end{document}