Burke - status code 415 indicates mismatch in the media type, which is expected because there is no Content-Type header
KeyboardSlappingMonkey - I think the request body should be something like the following (note the difference in the value format)
{"parameters":[{"name":"datacenterName","type":"string","value":{"string":{"value":"TestDC2"}}},{"name":"customerVMFolder","type":"string","value":{"string":{"value":"KamTestFolder"}}}]}
and you need to pass Content-Type header with value application/json;v=5.1.1
Hope this helps.