Are some big companies slow to arrange interviews, such as German companies?

It's true. It is not that big companies are slow, but that big companies are more formal. From talent selection to interview to employment, there are very professional processes and specialized departments and personnel, who are responsible at all levels. There are not many people in small companies, and only one or two people participate in the whole recruitment process, even the boss himself, so one person can make the final decision without screening at different levels, so it is fast. Germans are notoriously strict in the world, so it is normal to slow down. Please be patient.