While using Arduino Boards Version 1.6.12 the compilation and build process becomes incredibale slow? Same issue with Boards Version 1.6.13 and 1.6.14??
Plattform Win 8.1, 16 GB RAM and Intel Board.
Performance using IDE 1.6.8 and related Boards Version 1.6.8 on the same system is perfect.
And it is not caused by AV.
Some people have reported their antivirus causing compilation to be slow, but I don't know why that would be different between those versions. You might try TEMPORARILY disabling your antivirus to rule that out as a factor.
I've noticed on my computer(Win 7) that with recent versions when the IDE window is in the background the compilation process pretty much stops. I suspect this has something to do with thread priority level. It's pretty annoying because I like to multitask. Again, I don't see how that would be different between those versions.
You could try to set your antivirus to ignore the Arduino compilation process. You can see the commands that are run while compiling by doing File > Preferences > Show verbose output during: > compilation(check). I remember someone else trying ran into trouble trying to whitelist the temporary build folder but maybe you can figure out how to do that.