The CPU usage you showed in the screenshots is not very high. So let's start by investigating what do you mean by "slowness". It's very likely that your disks are saturated, causing everything to feel slow. It's a good hypothesis that the indexing server is the one causing it, but we've to collect more evidence first.
Go to Task Manager > Performance > Open Resource Monitor
. In the Resource Monitor, you'll see a tab called "Disk" where you can check which processes are using most of the disk I/O at that moment. Also check what is the "Response Time". Depending on your disks, you could see something 1-15ms as being quite normal or worse numbers like 200-2000ms. That would mean your disks are heavily saturated and you've identified the cause for the "slowness".
If the Indexing service is causing it, check a few things first:
- services.msc > Indexing Service => Ensure it's configured with "Automatic (Delayed Start)"
- Control Panel > Indexing Options => Ensure only the absolute necessary folders are indexed
If you added a new folder and/or there has been newer data added to an existing folder, you'll have to live with that and wait for the Indexing Service to finish it's job. You could try, but this is not guaranteed to make much difference, to give the Indexing Service "Below Normal" priority in Task Manager, but since the workload is I/O-bound it probably won't help that much.
If any other process is causing the excessive disk I/O, then you have to investigate that separately.