EtreCheck Report

Your Fusion (hybrid) drive is not entry-level but an extra-cost option that, at minimum, should do Write speeds of 500MB/sec of greater, and Read speeds in excess of 1000MB/sec. Its default performance is at minumum 10x faster than the entry-levels 5400, SATA 3G mech drive aApple selected as base storage.

The only Fusion drives that test slow are ones that are acting up, or ones suffereing software interference. Yours is atypically slow.

Before doing anything else I would completely diable you client-side VPN. Client-side VPNs are more hype than help anyway, Rerun the EtreCheck test without the VPN getting in the way and look under the "perforamnce" section near the end of the report. With that we can better see if the drive is truly sick, or only responding negatively to the inerference of unneeded software.

Your file system test failed. On your computer, it should have run in about 40 seconds or so. A brand new computer with a modern SSD can run this test in 9 seconds. EtreCheck terminated your test after 2 minutes.

Also, your entire report took 25 minutes to run. So the file system test failure was not enough to explain that.

Your CPU usage was 78% over 4 cores, with system at 65%. Yet EtreCheck's CPU usage doesn't reflect that. The system load report was very high at 10-18. This is normally 1-3. All that suggests that there is some bigger hardware failure. You should take this computer to an Apple Store or Authorized Service Provider for diagnostics and repair.

"Hard drive too slow - The hard drive in this computer is too slow." appears as a major factor

At 5400 RPM you can't expect much more for the HDD than you're getting. This appears to be a fusion drive (part HDD part SSD) and they were never known to be very "speedy".

Post the Etrecheck report.

Please read the following user tip and restate your question/problem in detail: 

     Writing an Effective Apple Support Communities Question - Apple Community

First, you have purchased one of the slowest Macs that Apple offered at the time of purchase: 8 GB of RAM and a 5400 rpm fusion drive. The only slower modes is the non fusion 5400 rpm drive.

You can improve boot time, application and file open time by cloning your boot drive to an external SSD. If you go that route I recommend you contact Customer Support at OWC (MacSales.com) so they can recommend the best model to meet your work needs, Mac capability and budget.

Unless you're using a true VPN tunnel, such as between you and your employer's, school's or bank's servers, they provide false security from a privacy standpoint.  Read these two articles: Public VPN's are anything but private and Former Malware Distributor Kape Technologies Now Owns ExpressVPN, CyberGhost, Private Internet Access, Zenmate, and a Collection of VPN “Review” Websites.  Additionally they can slow down internet access.

I don't see any of the usual suspects in the report. My previous reply stands as my recommendations to improve speed.