From the configuration shared in OP, the dbcache is set to 20000 which is way too much, in my opinion.
If he has 32GB of RAM and more, there's no harm on using a high cache size.
The problem in the config is
par=15 which limits his system on using 15cores while the default "0" will use all available cores if needed.
For the issue, OP might had just started the -reindex when he posted this thread.
At which point that there're no signature validation required for earlier blocks thus wont require a lot of CPU usage.
If not, there must be a bottleneck somewhere.