how to decrease the docker image layers latency during the image build step?

I am following the Microsoft document to create a custom image of vsts-agent on top of ubuntu and install the required capabilities.Since our environment is not having internet enabled, we used certain debian packages to install the capabilities and which resulted in multiple tasks in Docker file such as"COPY,"ENV setup for different apps,

Since we have these much steps, each is getting created in separate layer and which is causing vey slow image build.

FROM ubuntu:18.04#2-Enable Ubuntu PackagesCOPY ./sources.list /etc/apt/#3- Install basic SoftwaresENV DEBIAN_FRONTEND=noninteractiveRUN echo "APT::Get::Assume-Yes \"true\";" > /etc/apt/apt.conf.d/90assumeyesRUN apt-get update && apt-get install -y --no-install-recommends \    ca-certificates \    curl \    wget \    jq \    git \    iputils-ping \    libcurl4 \    libicu60 \    libunwind8 \    netcat \    telnet \    libssl1.0 \    python \    python3 \    nodejs \    python3-setuptools \    python3-pip    vim \    openjdk-11-jdk-headless \    gnupg \    make \    yarn\    apt-transport-https \    lsb-release \&& rm -rf /var/lib/apt/lists/*    #4. Copy Offline Packages    COPY ./sw/* /tmp/    #4-Install AzureCLI    RUN  curl -sL https://packages.microsoft.com/keys/microsoft.asc | gpg --dearmor | tee /etc/apt/trusted.gpg.d/microsoft.gpg > /dev/null    RUN AZ_REPO=$(lsb_release -cs) \&& echo "deb [arch=amd64] https://packages.microsoft.com/repos/azure-cli/ $AZ_REPO main" | tee /etc/apt/sources.list.d/azure-cli.list \&& apt-get update \&&  apt-get install azure-cli      #Installl helm,docker, googlechrome and kubectl    RUN  tar zxvf /tmp/helm-v3.8.2-linux-amd64.tar.gz  && mv /linux-amd64/helm /usr/local/bin/ && mv /tmp/kubectl /usr/local/bin/ \&&  apt install /tmp/google-chrome-stable_current_amd64.deb \&&  apt install /tmp/containerd.io_1.6.9-1_amd64.deb \&&  apt install /tmp/docker-ce-rootless-extras_20.10.9_3-0_ubuntu-bionic_amd64.deb \&&  apt install /tmp/libslirp0_4.6.1-1build1_amd64.deb      \&&  apt install /tmp/docker-ce_20.10.9_3-0_ubuntu-bionic_amd64.deb \&&  apt install /tmp/docker-compose-plugin_2.6.0_ubuntu-bionic_amd64.deb \&&  apt install /tmp/pigz_2.6-1_amd64.deb \&&  apt install /tmp/docker-ce-cli_20.10.9_3-0_ubuntu-bionic_amd64.deb \&&  apt install /tmp/docker-scan-plugin_0.9.0_ubuntu-bionic_amd64.deb \&&  apt install /tmp/slirp4netns_1.0.1-2_amd64.deb    #8-install maven 3.8.6    RUN mkdir -p /usr/share/maven /usr/share/maven/ref \&& tar -xzf /tmp/apache-maven-3.8.6-bin.tar.gz -C /usr/share/maven --strip-components=1 \&& echo "Cleaning and setting links" \&& rm -f /tmp/apache-maven.tar.gz \&& ln -s /usr/share/maven/bin/mvn /usr/bin/mvn        # 8.1- Define environmental variables required by Maven, like Maven_Home directory and where the maven repo is located        ENV MAVEN_HOME /usr/share/maven \            TARGETARCH=linux-x64 \            MAVEN_CONFIG "$USER_HOME_DIR/.m2" \            JAVA_HOME /usr/lib/jvm/java-11-openjdk-amd64        #11- Agent Installation        WORKDIR /azp        COPY ./vstsagent/ .        COPY ./start.sh .        COPY ./docker.sh .        RUN chmod +x start.sh docker.sh        ENV TARGETARCH=linux-x64        # Can be 'linux-x64', 'linux-arm64', 'linux-arm', 'rhel.6-x64'.        ENV TARGETARCH=linux-x64        ENV JAVA_HOME=/usr/lib/jvm/java-11-openjdk-amd64        ENV JAVA_HOME_11_X64=/usr/lib/jvm/java-11-openjdk-amd64        ENV MAVEN_HOME=/usr/share/maven        COPY policy-rc.d /usr/sbin/policy-rc.d        RUN dpkg -i /tmp/docker-ce_20.10.9_3-0_ubuntu-bionic_amd64.deb        COPY ./extensions/ /root/.azure/        RUN dpkg -i /tmp/google-chrome-stable_current_amd64.deb        RUN apt install -y --fix-broken        COPY ./sw/zip/* /tmp/zip/        WORKDIR /tmp/zip/        RUN dpkg -i zip_3.0-11_amd64.deb unzip_6.0-21ubuntu1_amd64.deb        WORKDIR /azp/_work        COPY ./tools .        RUN mkdir /root/.m2        WORKDIR /root/.m2        COPY ./settings.xml .        WORKDIR /root        COPY ./.npmrc .        COPY ./jf .        COPY ./config /root/.kube/        COPY ./docker-compose /usr/local/bin        COPY ./daemon.json /etc/docker/        RUN sed -i 's/"$@"/"$@" --no-sandbox/' /opt/google/chrome/google-chrome        ENV JFROG_CLI_HOME /root        ENV TESTCONTAINERS_RYUK_DISABLED=true        WORKDIR /azp        CMD ["./docker.sh"]        ENTRYPOINT ["./start.sh"]

So in the below sample, can we segregate repeating tasks to one layer so that the imagebuild step will be fast ?

• Also is it allowed to start the vsts-agent without root user? if yes, how I can achieve the same using normal user?