Are you doing every optimization in the
wiki?
I have a 4th gen with more cameras than you and BI idle is at 10% and will jump to 25% or so with a lot motion.
I also run DeepStack and OpenALPR on it for two cameras and total idle is 20%.
I get a weird phenomenon a few hours a day where the nooks and crannies of the asphalt glimmer and OpenALPR sees it at motion and that will peak the CPU at times, but I have knocked a lot of motion out with exclusion and inclusion zone in OpenALPR.
I got a 1030 GPU recently to try to offload OpenALPR too but it made the CPU % worse and OpenALPR would time out, so now I use it for DeepStack and it brought the ms times down a lot.
But yes OpenALPR is a resource hog. What resolution and FPS are you using?
If too high, I would suggest playing with that. In many instances 720P and 10FPS still works and brings down CPU a lot.