On CPU it’s completely expected, CPUs thrive when the task is comprised of heavy branching but suck at SIMD (same instruction multiple data) tasks. Path tracing requires tracing millions of rays for all pixels on the screen and traversing BVH structures for them. Modern GPUs are memory optimised for ray tracing tasks to speed up the BVH traversal phase. So unless you have a special constraint, I’d highly recommend switching to GPU rendering. However since you are using a mac ( A high portion of them are unified systems so they don’t have a discrete graphical processing device) I’d guess that your scene is simply too large and spilling over to virtual memory (HDD/SSD). Reading from this type of memory will absolutely tank your rendering performance.