Object field vs Individual field

I have two fields "support.agent" and "support.resolution".
If I can map these field as an Object type, I'll be able to fetch them together and also provides more readability

"support": {
         "properties": {
            "agent": {
               "type": "keyword"
            },
            "resolution": {
               "type": "keyword"
            }
         }
      }

What if I map them as two individual fields, something like this

"support:agent": {
  "type": "keyword"
},
"support:resolution": {
  "type": "keyword"
}

Is there any performance difference in using object field-type vs individual fields?

I'm not sure we performance test down to that level. I'd suggest you try it and see how it works for you.