This problem has occurred since version 9 on one of my two computers, but only when I disabled the external monitor and used the laptop's LCD. Normally I extend the desktop across the external monitor (1920x1200, main display having the Windows taskbar) and the laptop LCD (1920x1080). In the dual-monitor configuration there is no problem.
Today I installed Visual Studio 2015 Community Edition on a second computer where I never noticed any problems before. I immediately noticed the delays in Mathematica after the installer was done. Both systems are laptops running Windows 7, Mathematica version 10.0.2. The second system has three displays: two identical 1920x1080 monitors + laptop LCD at 1920x1080. Resetting Mathematica to default configuration didn't help, nor did updating the display drivers. Disabling the laptop's LCD solved the problem. I suspect that Visual Studio installed some incompatible shared DLL's or did something to the multi-monitor configuration that Mathematica didn't like.
Problem Occurs No Problem
Computer 1 only laptop LCD active LCD + 1 external display active
Computer 2 all three displays active 2 external displays active