We have been building our translations with Qt 5.13 on a windows machine with

– The C compiler identification is MSVC 19.24.28319.0
– The CXX compiler identification is MSVC 19.24.28319.0

With the same windows setup, but with Qt 5.15 our translations process takes ~45 minutes now, instead of the ~10 seconds with Qt 5.13.

One of the big differences between both setups is that Qt 5.15 was built on the machine using Conan.
When using Qt 5.15 prebuilt binaries there is no performance problem.

With Qt 5.13 we were using pre-built binaries from the installer.

The same setup on the Linux machine takes ~10 seconds.
There are about 1000 strings to be translated in 12 languages.