I downloaded the Windows 10 technical preview, and tried to run League of Legends. It wasn't running (gave an error message, something about DirectX), so I went to the NVIDIA control panel and made League run on integrated graphics. This worked, but now League is running VERY slowly. Is there a fix to this? (besides downgrading back to Windows 8.1)
Technical previews are not designed for end users, it is for software designers (like the people who write those drivers). That way when Windows 10 has its general release drivers will be available day one.
The only solution is time. All you can do is wait for Nvidia to release a driver (keep a eye on their Beta drivers, it will be there first).
Apparently, this is only a problem with the Razer Blade 2014. All other laptops don't have any problems according to other users. There is no fix for this currently, guess the best thing is to wait until Razer comes out with an update.