30 page document takes one hour to compile

I know that there are multiple questions of the kind "file takes too long to compile", but one whole hour for a 30-pages document seems abnormal to me. I’m using a custom LaTeX package, which is most likely to be the cause. The document includes hundreds of things like this:

newcommand{CARD}[2][]{%
    raisebox{-2 pt}{%
        begin{tikzpicture}
            StrLeft{#2}{1}[@@color]
            StrRight{#2}{1}[@@number]
            cardsetup{#1, color=@@color, number=@@number}
            draw[bordercolor, line width = 0.9 pt] (-0.36, -0.24) rectangle (0.36, 0.24)
            (0,0) node {nsymbol ! csymbol}
            cclue nclue;
            carddefault
        end{tikzpicture}%
    }%
}

where nsymbol csymbol cclue nclue are all instances of

newcommand{thing}{scalerel*{%
        defsvgwidth{10 pt}%
        import{thing.pdf_tex}%
    }{Xrule[0ex]{0pt}{1pt}}%
}

Any idea about how to speed up things?