Simple question about performance troubles

[defs]

I have trouble with this simple application. It will respond very slowly (processor usage is over 90%) if I have background picture or just pure Rectangle (id: background in example bellow) before button, if I comment this background rectangle, application would react quickly, but if I add "enable.layers: true" to root item, slow response would be come back .
Where is the problem?
I would like to have background picture and fast response on clicking.
I am running this example on Raspberry Pi 3.

import QtQuick 2.3


Item {
    id: root
    visible: true
    width: 800
    height: 480


    Rectangle {
        id: background
        anchors.fill: parent
        smooth: true

    }

    
    Rectangle {
        id: button
        width: 200 ; height: 123

        anchors.centerIn: parent

        smooth: true
        radius: 8

        //color the button with a gradient
        gradient: Gradient {
            GradientStop {
                position: 1.0
                color: {
                    if (mouseArea.pressed)
                        return "red"
                    else
                        return "chartreuse"
                }
            }
            GradientStop {position: 0.0; color: "paleturquoise" }
        }


        MouseArea {
            id:mouseArea
            anchors.fill: parent
            onPressed: {
                //handler.turnOn()
            }
            onReleased: {
               // handler.turnOff()
            }

        }
    }
}

UPDATE: When running this example with qmlviewer from terminal it works fast as expected (in that case have to use "import QtQuick 1.1" instead "2.3". When running with qmlscene from terminal or with QQuickView from C++ this app respond very bad on clicking button,