With that method, the "krusader-build" folder way is used, as it's also followed in:
- The Release Howto: https://phabricator.kde.org/w/krusader/release-howto/
- The INSTALL file: https://commits.kde.org/krusader?path=INSTALL
- The method that Davide Gianforte wrote in the "krusader-devel" mailing list.
Additionally, as Alex Lohnau proposed, use make -j$(nproc).