What is the right course of action here?

Your answer to slow down and wait is correct because in this traffic situation, you must yield to vehicles already on the right or waiting at the intersection. According to German traffic rules, when you approach an intersection without a priority sign and there are vehicles on your right, you must give way to them. Slowing down and waiting ensures safety and compliance with the "right before left" (rechts vor links) rule. Simply continuing at reduced speed or queuing behind without slowing sufficiently might not guarantee you yield properly, which is why waiting is the safest and legally correct option.