unzip to here /opt/Trolltech/Qt5.15.2/raspi
no need to make... 7z has all it needs to run..
if you want to build other modules then unzip qtbase.zip and edit configure-me.sh

QMake Kit Dir: /opt/Trolltech/Qt5.15.2/raspi/qt5 /qmake
C compiler Dir: /opt/Trolltech/Qt5.15.2/raspi/tools/gcc-linaro-7.4.1-2019.02-x86_64_arm-linux-gnueabihf/bin/arm-linux-gnueabihf-gcc
CPP compiler Dir: /opt/Trolltech/Qt5.15.2/raspi/tools/gcc-linaro-7.4.1-2019.02-x86_64_arm-linux-gnueabihf/bin/arm-linux-gnueabihf-g++
sysroot: /opt/Trolltech/Qt5.15.2/raspi/sysroot