Bootstrap 15 columns

HTML

<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.2/css/bootstrap.min.css">
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.2/js/bootstrap.min.js"></script>
<div class="container-fluid">
    <div class="row">
        <div class="col-xs-4">
            <div class="row">
                <div class="col-xs-3 fixed">1</div>
                <div class="col-xs-3 fixed">2</div>
                <div class="col-xs-3 fixed">3</div>
                <div class="col-xs-3 fixed">4</div>
                <div class="col-xs-3 fixed">5</div>
                <div class="col-xs-3 fixed">5</div>
                <div class="col-xs-3 fixed">5</div>
                <div class="col-xs-3 fixed">5</div>
                <div class="col-xs-3 fixed">5</div>
                <div class="col-xs-3 fixed">5</div>
                <div class="col-xs-3 fixed">5</div>
                <div class="col-xs-3 fixed">5</div>
                <div class="col-xs-3 fixed">5</div>
            </div>
        </div>
        <div class="col-xs-4">
            <div class="row">
                <div class="col-xs-3 fixed">6</div>
                <div class="col-xs-3 fixed">7</div>
                <div class="col-xs-3 fixed">8</div>
                <div class="col-xs-3 fixed">9</div>
                <div class="col-xs-3 fixed">10</div>
            </div>
        </div>
        <div class="col-xs-4">
            <div class="row">
                <div class="col-xs-3 fixed">11</div>
                <div class="col-xs-3 fixed">12</div>
                <div class="col-xs-3 fixed">13</div>
                <div class="col-xs-3 fixed">14</div>
                <div class="col-xs-3 fixed">15</div>
            </div>
        </div>
    </div>
</div>

CSS

.col-xs-3.fixed {
    width:10%;
    border:1px solid #000;
}