Very high CPU usage in VMware environment

Hello,
We have an ongoing issue with CPU usage for the RDS server. We have Office 365 , a small telnet program , pdf viewer...
not very much going on. We have a license for 55 users but generally only see 25 - 30 users concurrently.
At this time I have only 1 RDS server running.
After a reboot server will run fine for a couple weeks then exhibit the same issue. I have seen an article stating
that you can have too many cpu's assigned to the VM. I have 4 cpu's and 24GB memory. Would like to determine if we need more
memory , less CPU etc. to help with this.
Maybe we should add another RDS server for load balance? Can parallels support help with that addition?
Thank you