Well, Twine editor 2.4.0 is coming “soon”, so hopefully that should resolve the issues with the editor slowing down as the game gets huge that Greyelf mentioned.
As for the compiled game getting slow, you might want to check out the comments in the “Any tips on optimization?” thread. You might also want to check out the “FlagBit code” section of my Twine/SugarCube sample code collection. That section is somewhat based on the “bitwise operators” part I mentioned there.
Hope that helps! 