I couldn't reproduce any significant performance decrease on Windows.

Could you please check if the problem still exists if you change in .../qt-scripted-modules/DataProbe.py

From this:
...
def processEvent(self,observee,event):

TODO: use a timer to delay calculation and compress events

insideView = False
ras = [0.0,0.0,0.0]
...

To this:
...
def processEvent(self,observee,event):
return

TODO: use a timer to delay calculation and compress events

insideView = False
ras = [0.0,0.0,0.0]

...

Andras

-----Original Message-----
From: slicer-devel-bounces@bwh.harvard.edu [mailto:slicer-devel-bounces@bwh.harvard.edu] On Behalf Of criskross
Sent: Tuesday, November 24, 2015 11:36 PM
To: SPL Slicer Devel <slicer-devel@bwh.harvard.edu>
Subject: Re: [slicer-devel] Slicer enormous performance loss caused by Data Probe

Hi Andras,

the problem doesn't exist when I change the code like you said.

This issue has been confirmed to be related to Mac OS 10.11 (El Capitan) and does not occur on 10.10 (Yosemite)

Possibly related issue: https://bugreports.qt.io/browse/QTBUG-47354