One of the main characteristics of virtual reality (VR) is immersion, which leads to comprehensive illusions of reality. Accordingly, VR is used in many applications like entertainment, marketing, and training. Especially in training applications, the effect of immersion on training success is still not entirely clear, since too much immersion may cause side effects such as users experiencing high mental demand whereas too little may disturb users' well-being. To further investigate the matter, we developed two virtual training environments, wherein users train a typical industrial assembly task either in low or high immersive VR. In a controlled pilot study, we additionally introduced a third condition, the control group, which justifies the necessity of the training. Immediately after the VR training session, each participant completed the corresponding real assembly task in which their performance was measured. Preliminary results from our pilot study show that participants trained in high immersive VR performed better, while negative side effects could not be detected.