Colloidal suspensions are essential and found in various nano- and micro-scale engineering and scientific fields, such as slurries in chemical engineering, colloidal photocatalysts in environmental remediation, and milk in food science. High concentrations are in high demand across various industries, such as for improving product quality and reducing transport costs by reducing the weight of suspensions. The development of a method to non-destructively evaluate particle properties (such as particle size distribution and aggregation degree) of high-concentration colloidal solutions is urgently needed. Light-scattering techniques have been extensively developed as promising tools for evaluating particle properties. Meanwhile, most developed techniques require sample dilution, with the volume fraction typically less than 5%. Thus, the method is still under development. For this development, simultaneous and appropriate modeling of the particle properties and light scattering, along with a fast solution method, is essential. In this study, a fast calculation method was developed based on the local monodisperse approximation to the dependent scattering theory (DST). Previously, we proposed a rapid method for polydisperse systems without particle agglomeration; here, we extended it to agglomerated systems. The DST describes the far-field interference between the scattered electric fields in dense colloidal systems. We successfully achieved a speedup of over 800 times in computation, while maintaining the same accuracy in describing the DST results. Our findings provide forward modeling for developing nanotechnology to evaluate the particle properties non-destructively using scattered light.