toDataURL() very slow

I have a report with charts and tables.
I am using the html2canvas with jsPDF to export this report to PDF file.

But the process is taking a long time, more than 11000ms.
I've tried to change the format, the quality, but nothing worked.

See below the code I used:

html2canvas($('#first-page'), {
    onrendered: function(canvas) {
        firstPage = canvas.toDataURL('image/jpeg', 0.5);
    },
    background: '#ffffff'
});

I'm doing something wrong or really is a problem?
How I can improve the performance?