August 2015 Windows Update for Vista Requires One Hour to Run to Completion

Is Microsoft throttling bandwidth for users running Windows Update on Vista machines to give a higher priority to Win 10 users?

I've run multiple Windows Updates since Patch Tuesday on 11-Aug-2015 and couldn't get them to run to completion on my 32-bit Vista machine until 16-Aug-2015.  There were no errors - it just reported that it was checking for updates and never finished, even if I let it run for over an hour.  Process Explorer showed svchost.exe constantly consuming ~50% of my CPU (i.e., complete saturation of one of my Intel Duo cores) and that a thread for the Windows Update service (wuauserv) was responsible for all that CPU activity.

I assumed that my Windows Update service was corrupted but after reading posts by other Vista users having the same problem (see ScousaJay's post *Windows Update Just Seems to Hang While Checking* in the Windows VistaForums for one example) I tried a manual update again on 16-Aug-2015.  Windows Update finally ran to completion and offered 17 important updates and one optional update for Silverlight but it took approx. 35 min before it reported that updates were available and the entire process, including the downloads, installs and monthly Malicious Software Removal scan, took almost a full hour.  A typical Patch Tuesday normally takes about 10 min on my machine from start to finish.

Here's what the CPU consumption looked like for my successful Windows Update of 16-Aug-2015, with the "Checking for updates..." phase running between the 70 and 35 min marks and re-start to complete the installation around the 15 min mark.

32-bit Vista Home Premium SP2 * Firefox 40.0.2 * IE9 * NIS 2014 v. 21.7.0.11

HP Pavilion dv6835ca, Intel Core2Duo T5550 @ 1.83 GHz, 3 GB RAM, NVIDIA GeForce 8400M GS