Template Redirect to /2015 to use page template

If you really want to override the yearly archive for 2015, then you can try the following:

add_filter( 'template_include', function( $template ) 
{
    //-------------------------
    // Edit this to your needs:
    //-------------------------
    $year = 2015; 
    $report_template = "tpl-annual-report-{$year}.php";

    //----------------------------------------------
    // Override the default yearly archive template
    //----------------------------------------------
    if ( 
           is_year()                          // Yearly archive
        && $year == get_query_var( 'year' )   // Target the year 2015 
        && $new_template = locate_template( [ $report_template ] ) 
    )
        $template = $new_template ;

    return $template;
} );

where your annual report template for the year 2015 is tpl-annual-report-2015.php.

More on the template_include filter in the Codex here.