I hope, colleagues you would not object me putting in my another 2 cents? ;-)
Two things may slow down the performance (whether it's Code Ref. search, or any other search through the files on disk, regardless):
1. Automatic updates (I hate them with passion because of that, but that's another topic altogether, let's not elaborate on it here).
2. HDD "energy saving" or "sleep" mode (for the lack of better word, coz memory ain't servin' me well at the moment).
The former lurks behind the scene and, upon arrival via Internet, "intercepts" the HDD and forces it to work for itself all but exclusively. Remedy? Do not log in to the Net unless you mean it.
The latter is the trade off for longer lasting battery in the autonomous mode in laptops: your HDD stops spinning, thus consuming less energy overall; however, once the "request for service" comes from CPU to the HDD - it needs some time to come out from that "sleep" mode, start and accelerate its rotation to gain its normal rotation speed.
Note that the HDD is "the culprit" in both cases. No wonder, however: it
is the slowest component in any computer - would not you agree? (

)
Regards,
Ilya