Ubuntu 20.04 LTS has Qt 5.15.2 in its official repos:
mkdir build && cd build ../configure -prefix /path/to/install -opensource -confirm-license -nomake tests make -j$(nproc) make install If you don't want to deal with Qt accounts or installers, use your system's package manager. Note: These may not be the exact 5.15.2 but close patch versions. qt5.15 download
sudo apt install qt5-default qtbase5-dev qtbase5-dev-tools Ubuntu 20
https://download.qt.io/archive/qt/5.15/5.15.2/qt-opensource-mac-x64-5.15.2.dmg qt5.15 download
brew install qt@5 This installs the latest Qt5 (likely 5.15.x). Pin it to prevent auto-upgrade.
git clone https://code.qt.io/qt/qt5.git cd qt5 git checkout 5.15 perl init-repository
md5sum qt-opensource-linux-x64-5.15.2.run Compare the output with the contents of the .md5 file.