Service Host: Local System (15) - HIGH CPU USAGE

Have a read through these threads:
http://www.tenforums.com/performance-maintenance/25606-high-cpu-usage.html
http://www.tenforums.com/performance-maintenance/14464-processes-causing-high-cpu-use-windows-10-a.html
http://www.tomshardware.com/forum/id-2777154/high-cpu-usage-windows-download.html
https://www.reddit.com/r/Windows10/comments/3g9rnr/windows_10_high_cpu_and_memory_usage/
http://www.drivethelife.com/windows-10/fix-high-ram-cpu-memory-usage-after-windows-10-update.html
http://news.softpedia.com/news/windows-10-high-cpu-usage-fix-490908.shtml

It'd help us further if we knew your systems specs.
 
If 15 (or some other number) is the PID, go to the Services tab in the Task Manager.

You will see 1 or more of the PID's that you're concerned with, go to Control Panel, Administrative Tools, click on Services.

One by one, stop or disable, then restart each service indicated, all the while keeping an eye on the Task Manager Performance Tab.

When the CPU's drop, that's your culprit.

Bill