In your case it helps a little optimization in proxy, or you can use "# time out settings"
location /
{
# time out settings
proxy_connect_timeout 159s;
proxy_send_timeout 600;
proxy_read_timeout 600;
proxy_buffer_size 64k;
proxy_buffers 16 32k;
proxy_busy_buffers_size 64k;
proxy_temp_file_write_size 64k;
proxy_pass_header Set-Cookie;
proxy_redirect off;
proxy_hide_header Vary;
proxy_set_header Accept-Encoding '';
proxy_ignore_headers Cache-Control Expires;
proxy_set_header Referer $http_referer;
proxy_set_header Host $host;
proxy_set_header Cookie $http_cookie;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-Host $host;
proxy_set_header X-Forwarded-Server $host;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
}