How to limit clock speed for CPU

Hi. I am creating VM's for proxmox, and I see there is a drop down for different types of CPU's, by default it just uses a core of the regular CPU, but what if I want to limit it?

I have a 1230v2 i7 in my server, and by default the clock speed is 3.2 ghz I believe. I want to limit this down to half of a core for one of my clients, to give him around 1.5ghz or 1.6ghz of processing power. Is there an option to do something like this in proxmox? Do I need to use a different CPU architecture type?

Thanks.