That is expected result
X11 protocol is inefficient for drawing modern apps, not to mention the overhead of SSH encryption and decryption.
You can speed up X11 forwarding, but don't put your hopes too high.
- Enable Compression in the Connection tab of profile settings.
- Enable trusted X11 forwarding, set
ForwardX11Trusted
option toyes
in Advanced tab.
I answer this in another post of your:
Yang