There's a couple of potential problems. The i5 is a 2-core CPU, so you definitely don't want more than 2 cores assigned to the VM - and 1 if you can get away with it.
Next check activity monitor on the host and task manager in the guest - can you find the process that's causing the the high CPU usage? Two common culprits in the guest, are if you have antivirus scans configured (disable those and use active protection only - scanning is really no longer needed). Likewise, disabling system restore can help with high loads.
