Just an addition to what I've written before, I copy & paste from the link/Issue, because it describes better than I just did, what we *think* is the Issue - but we cannot be 100% sure because we do not know how Intel Drivers operate!:
"Systems with nVidia or AMD GPU's show no FPS difference between the old and new launcher.
However, Intel GPU powered systems drop to 1/3 or even 1/4 the framerate with the new launcher.
Since issue previously existed on 3rd party launchers such as MagicLauncher, sp614x (coder of Optifine and MagicLauncher) and I have narrowed the culprit down to the fact that the new launcher uses a separate process to run the game while the previous Minecraft.exe launcher ran the game inside the same process.
I have theorized that Intel drivers no longer recognize the game as a 3D application when this happens thus and limits GPU utilization, but it's hard to know for sure without more knowledge about how Intel drivers operate."