In your command, you mentioned release data as "ESXi-6.0.0-20151004001-standard" this will upgrade to standard or retain free version? (vSphere Hypervisor 6). Please clarify.
This is just the name of the image profile and has nothing to do with with free Hypervisor vs. paid licensed version. Your current image profile name is also "*-standard". Software-wise there are no different "free" and "paid/standard" software editions anyways, it's the same install and just a matter of which license you use on a host.