CPU usage too high

My vps is Windows 2012 R2 standard. CPU: E5-2670 v2 to 2.5G (4 cores), no L1 cache. 6 GB of RAM.
I have 20 private proxies.
I install GSA SER at 100 threads, decreases the processor when the value exceeds 80%. Ignore all blacklists. Ignore all sites contain sex words.
With almost all the platforms and checked lists of SeRocket, no public relations limit, no limit of obl.

Most of the time, GSA SER runs at 20 threads, 90% of the CPU, 500 MB of RAM, 15 vpm. I think that he eats too much CPU.
Is this normal? Or I have problems in the settings. Please help, thank you.