Real-time global illumination rendered with low variance remains a persistent challenge. Many engines employ irradiance probes as a relatively cheap technique, but constrained computational budgets often lead to flickering artifacts in rendered images. In this paper, we propose spatial multiple importance sampling, which reuses ray-surface intersection data among real-time irradiance probes to significantly reduce flicker caused by variance, enabling efficient computation in complex scenes under limited ray tracing budgets. Moreover, our approach incorporates a probe selection mechanism to enhance reuse efficiency and a visibility estimation method to mitigate bias. Experimental results demonstrate that our method significantly reduces variance at a fixed ray tracing cost, delivering high-quality, stable outputs in real-time scenarios.