Documentation says the key "vm.vmemory.size" exists for "Virtual Memory": https://www.zabbix.com/documentation/3.2/manual/config/items/itemtypes/zabbix_agent/win_keys.

Also, the Windows Default Template delivered with Zabbix Server 3.2.3 (fresh install) uses this item key, for the item with name "Free virtual memory, in %" (item key: "vm.vmemory.size[pavailable]").

Nevertheless, the Windows Agent (version 3.2.0 running, latest stable) seems not to support this key:

aanton@zabbix:~$ zabbix_get -s 192.168.1.3 -k vm.vmemory.size
ZBX_NOTSUPPORTED: Unsupported item key.