We have the exact same issue. Boot times is more than an hour and really hurting our patch cycles, and general trust when downtime occurs.
When the clusters are available for ssh login no Virtual Systems are online for maybe 30 minutes.
After this Virtual Systems are loaded sequentially for another 30 minutes.
So in total we use 1h plus to boot a node. We see no performance related issues with top, iotop or other debugging tools.
Actually the box is idle until policies start loading. We do see that the process 'cgroup' is intermittently using some CPU.
We mostly use Lenovo 850p servers with 32 cores, and 256gb ram running a mix of r80.40 and r81.10
Not sure why I have not created a TAC case already. I will do that.