Logstash Grok match to last index unti begin of UserAgent

I have this log message:

"sid-cmascioieiow89322&New*Sou,th%20Skvn%20and%20ir&o,n%20Age,Mozilla/5.0 (Linux; Android 6.0; CHM-U01 Build/HonorCHM-U01) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/52.0.2743.98 Mobile Safari/537.36"

And the pattern:

"(?[^&])&(?[^,]),%{GREEDYDATA:User_Agent}"

The problem is p2 sometimes contains zero or one or more then one comma. I want to match to the last comma before UserAgent because UserAgent some time contains commas.

This is the grok debugger link: https://grokdebug.herokuapp.com/

Now:

{
    "p1": [
        "sid-cmascioieiow89322"
    ],
    "p2": [
        "New*Sou"
    ],
    "User_Agent": [
        "th%20Skvn%20and%20iro,n%20Age,Mozilla/5.0 (Linux; Android 6.0; CHM-U01 Build/HonorCHM-U01) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/52.0.2743.98 Mobile Safari/537.36"
    ]
}

I want like this:

{
    "p1": [
        "sid-cmascioieiow89322"
    ],
    "p2": [
        "New*Sou,th%20Skvn%20and%20ir&o,n%20Age"
    ],
    "User_Agent": [
        "Mozilla/5.0 (Linux; Android 6.0; CHM-U01 Build/HonorCHM-U01) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/52.0.2743.98 Mobile Safari/537.36"
    ]
}

Thank you for your help.