I admit this is really off-topic, but I searched this forum, the entire internet and every corner of my brain wasting hours figuring this out. And I admit blaming Arduino somewhere along the way... Sorry.
What I experienced: My Dell M4800 compiles my sketch in 5-8 seconds at work and 30+ seconds at home. I thought it related to some missing network drive, but it did not. I thought it related to some environmental parameter or the fact that Arduino recompiles all libraries into new temp folders - even libraries not used - every time i build the sketch. It does not - even though I do not understand the need to build everything every time....
The reason is simple. When at home, my laptop runs on a small 65W power supply; at work a 3 times more powerful supply. It seems that the laptop adapts to this by slowing down. I have not noticed low performance in other applications, but with Arduino it is clear.
I hope this is helpful to other frustrated Arduinoficados.