var counter = 2;
var imagesCount = 15;
var images = new Array();
for(var i=1; i<=imagesCount; i++){
    images[i] = "url(images/main/image"+(i)+"h.jpg)"
}

function changeImage(){
    setTimeout(
        function () {
            changeBackgroundimage(images[counter]); 
        }, 7000
        );
}

function changeBackgroundimage(newImageSrc){
    document.getElementById("image").style.backgroundImage = newImageSrc;
    updateCounter();
    changeImage();
}

function updateCounter(){
    if (counter != (imagesCount)){
        counter  = (counter % (imagesCount+1)) + 1;
    }
    else counter = 1;
}