Intercell interference (ICI) significantly degrades performance in Long-Term Evolution (LTE) heterogeneous networks (HetNets), particularly at cell edges. This study presents a measurement-driven analysis using 15-day drive-test data from the University of Port Harcourt, Nigeria, across distances of 100–1500 m. Results show SINR improving from 10.5 dB to 24.2 dB and throughput increasing from 25.03 Mbps to 61.85 Mbps (147% gain) as interference decreases. Analytical models closely matched measurements (0.29 dB SINR, 0.68 Mbps throughput error). Findings confirm the strong impact of ICI on QoS and emphasize the need for mitigation techniques such as eICIC and coordinated beamforming.