Optical fibers are the backbone of high-capacity communications, with submarine links carrying most of the international traffic. Modern systems rely on coherent technology, where chromatic dispersion is digitally compensated at the receiver (uncompensated transmission, UT). In contrast, legacy IMDD systems relied on dispersion compensation along the link (dispersion-managed, DM). The continued use of DM links motivates the development of rapid quality-of-transmission evaluation tools. Although optical transmission is an aggregated process, our simulations show that it can be accurately approximated with a spectrally and spatially disaggregated approach. The proposed model quantifies the non-linear interference generated by each pump using the GN model, the correlation coefficient accounting for coherency accumulation between spans, and the signal Gaussianization coefficient.