We've just pushed an update to the 'beta' branch (or "Beta" in Steam).
This includes two big updates:

• Improved memory management
• Keyboard shortcuts in Sketch-mode

We want to have more time to test the impact that the new memory management will have, which is why it has not rolled out to everyone just yet. Though initial reports are positive and it appears to be a little "snappier" now.

Instructions for enabling 'beta' are here:
http://steamcommunity.com/app/280680/discussions/3/540744475062163773/

Please leave feedback in the comments below, or the Beta branch discussion forum :D