\documentclass[review]{elsarticle}
\usepackage[a4paper,width=150mm,top=26mm,bottom=26mm]{geometry}
\usepackage{graphicx}
\usepackage{caption}
\usepackage{subcaption}
\newsavebox{\bigpicturebox}
%\setlength\abovecaptionskip{0pt} % <=== delete
\begin{document}

\begin{figure}[h]
    \centering
    \sbox{\bigpicturebox}{%
        \begin{subfigure}[b]{.5\textwidth}%
        \scalebox{1}[1]{\includegraphics[width=\linewidth]{A.png}}%
        \caption{Magnitude (3D)}%
        \end{subfigure}%
    }
    \newlength{\maxht}% <==== added
    \settoheight{\maxht}{\usebox{\bigpicturebox}}% <==== added
    \usebox{\bigpicturebox}\hfill
    \begin{minipage}[b][\maxht][s]{.45\textwidth}% <==== changed
        \begin{subfigure}{.5\linewidth}
            \centering
            \includegraphics[height=.4\maxht]{A.png}% <==== changed
            \caption{u (3D)}
        \end{subfigure}\hfill
        \begin{subfigure}{.5\linewidth}
            \centering
            \includegraphics[height=.4\maxht]{A.png}% <==== changed
            \caption{v (3D)}
        \end{subfigure}\vfill% <==== changed
        \begin{subfigure}{.5\linewidth}
            \centering
            \includegraphics[height=.4\maxht]{A.png}% <==== changed
            \caption{u (2D)}
        \end{subfigure}\hfill
        \begin{subfigure}{.5\linewidth}
            \centering
            \includegraphics[height=.4\maxht]{A.png}% <==== changed
            \caption{v (2D)}
        \end{subfigure}%
    \end{minipage}
    \caption{Caption of the Figure.}
    \label{Fig. 3}
\end{figure}

\end{document}