This problem is pretty annoying. You enter one letter in the vSphere console and it's repearing X times. You can resolve this problem in 2 ways:
First of all power down your VM.
Edit your vmx file and add this line at the end:
keyboard.typematicMinDelay = "2000000"
2. In vSphere:
Right click on the virtual machine and go to Edit Settings
Click Options > General > Configuration Parameters
Click Add Row
Name field: keyboard.typematicMinDelay
Value field: 2000000
Confirm by clicking OK.
Power on your VM!