VNC connection is too slow to operate

I use VNC Viewer to connect to the Respeaker Core v2 , and unfortunately the operation responds very slowly.

When I click the menu on VNC Viewer, it takes about 3 minutes to show the menu items.

The connection is based on 1Gb WLAN,and

①how can i improve the vnc response speed?

②Can i use the hdmi as the graphic output interface? And How?

After updating the os to respeaker-debian-9-lxqt-sd-20180610-4gb.img, the VNC connection become faster than the one of the respeaker-debian-9-lxqt-sd-20180319-4gb.img. Something may be optimized.

Hi, we optimized more than 60% codes from u-boot to kernel to improve the performance for respeaker-debian-9-lxqt-sd-20180610-4gb.img. thanks.

Seeed techsupport team