Enable the following options on all Terminal Servers in your farm. Under Computer Configuration\Administrative Templates\Windows Components\Remote Desktop Services\Remote Desktop Session Host\Remote Session Environment enable the following:
Configure RemoteFX
Optimize visual experience when using RemoteFX. Set to Medium Default.
Set Compression algorithm for RDP data. Set to Optimize to use less network bandwidth.
Optimize Visual experience for Remote Desktop Services sessions. Set to Rich Multimedia.
Configure image quality for RemoteFX Adaptive Graphics (Image Quality set to Medium).
Configure RemoteFX Adaptive Graphics. Set to Let the system choose experience for network conditions.