We've been running into an issue where machines use lots of memory and take a while to scan for software updates.
Software updates scan runs inside svchost.exe which means that you can see that process use up to 1,5gb of memory and taking up to 30 minutes.
This happens more on machines with only 2 Gb of Ram and with 32 bits operating systems and mostly Windows 7.
For more details check :
Following the above article and cleaning you're wsus is a best practice and will improve all your clients performance!
Beside that we have released the Windows Update Agent fix under the following:
3050265, Windows Update Client for Windows 7: June 2015, http://support.microsoft.com/kb/3050265/EN-US