\documentclass[a4paper]{article}
\usepackage{tikz}
\usepackage{multicol}
\usepackage[separateanswersheet,answers,noshuffle]{automultiplechoice}
% \AMCboxStyle{shape=oval}

\begin{document}
\AMCtext{draft}{}
\AMCtext{message}{}
\begin{question}{preza15} first \begin{choices}\correctchoice{a1}\wrongchoice{a2}\wrongchoice{a3}\wrongchoice{a4}\end{choices}\end{question}
\begin{question}{prezb1} second \begin{choices}\wrongchoice{a1}\wrongchoice{a2}\correctchoice{a3}\wrongchoice{a4}\end{choices}\end{question}
\begin{question}{prezc2} third \begin{choices}\wrongchoice{a1}\wrongchoice{a2}\correctchoice{a3}\wrongchoice{a4}\end{choices}\end{question}
\begin{question}{prezd3} fourth \begin{choices}\wrongchoice{a1}\wrongchoice{a2}\correctchoice{a3}\wrongchoice{a4}\end{choices}\end{question}
\begin{question}{preze4} fifth \begin{choices}\wrongchoice{a1}\wrongchoice{a2}\wrongchoice{a3}\correctchoice{a4}\end{choices}\end{question}
\begin{question}{prezf5} sixth \begin{choices}\correctchoice{a1}\wrongchoice{a2}\wrongchoice{a3}\wrongchoice{a4}\end{choices}\end{question}
\begin{question}{prezg6} seventh \begin{choices}\correctchoice{a1}\wrongchoice{a2}\wrongchoice{a3}\wrongchoice{a4}\end{choices}\end{question}
\begin{question}{prezh7} eighth \begin{choices}\wrongchoice{a1}\correctchoice{a2}\wrongchoice{a3}\wrongchoice{a4}\end{choices}\end{question}
\begin{question}{prezi8} ninth \begin{choices}\wrongchoice{a1}\correctchoice{a2}\wrongchoice{a3}\wrongchoice{a4}\end{choices}\end{question}
\begin{question}{prezs9} tenth \begin{choices}\wrongchoice{a1}\wrongchoice{a2}\wrongchoice{a3}\correctchoice{a4}\end{choices}\end{question}
\begin{question}{prez10} eleventh \begin{choices}\wrongchoice{a1}\wrongchoice{a2}\correctchoice{a3}\wrongchoice{a4}\end{choices}\end{question}
\begin{question}{prez1f1} twelfth \begin{choices}\correctchoice{a1}\wrongchoice{a2}\wrongchoice{a3}\wrongchoice{a4}\end{choices}\end{question}
\begin{question}{prez1sdf2} thirteenth \begin{choices}\correctchoice{a1}\wrongchoice{a2}\wrongchoice{a3}\wrongchoice{a4}\end{choices}\end{question}
\begin{question}{prez1fs3} fourteenth \begin{choices}\wrongchoice{a1}\wrongchoice{a2}\correctchoice{a3}\wrongchoice{a4}\end{choices}\end{question}
\begin{question}{prez1sdf4} fifteenth \begin{choices}\wrongchoice{a1}\wrongchoice{a2}\correctchoice{a3}\wrongchoice{a4}\end{choices}\end{question}
\makeatletter
\def\AMCformQuestion#1{#1.}
\def\AMCformAnswerA#1{\addtocounter{AMC@ncase}{1}#1}
\renewcommand\AMC@answerBox@[4]{%
\ifAMC@catalog%
    \AMC@logchar{#1}{#4}%
\fi%
\ifx #2\AMC@checkedbox \AMCchoiceLabelFormat{#1}\fi%
}
\makeatother

\hrule
\vspace{5mm}
{\Large ANSWER KEY}
\AMCformBegin
\begin{multicols}{3}
\AMCform
\end{multicols}

\end{document}