SuperKEKB is an electron-positron collider providing beam to the Belle-II experiment. The design luminosity has not yet been achieved, partly due to limited injection efficiency in both rings, which limits the achievable beam current. In addition, the injection process generates significant background in the Belle-II detector, requiring vetoes during data taking that reduce the detector efficiency. In order to improve the understanding of these issues, the injection process at SuperKEKB has been simulated using the Xsuite simulation framework, including detailed multi-turn tracking and particle-matter interactions in the collimators. The results of these simulations have been used as input for a Belle-II detector simulation to estimate the resulting background levels. This paper presents the simulation methodology and the comparison with experimental data, collected during the 2025 run, as a prerequisite for future applications of the simulation framework including further optimization of the background at SuperKEKB as well as similar studies for future lepton colliders.