Hardware and performance

So you are playing the role of Bob Crachit and want help talking to the Scrooge's at a Uni?  Hmmmmm  ....

Clues ... 'unmanaged VM' ... Windows 2012 R2 ... venturing a guess the Moodle has also been 'unmanaged'.

Why it failed requires more info and inspection of logs of Apache, MySQL, PHP.

Only you can do that ... no one has access to your 'server' and don't believe anyone will ask for access to it (no Vulcan  Mind Meld possible!).   So guess you are asking for someone here in  community to write up justifcation for upgrading?  Uhhh ... don't they call that 'consulting'?

So far we know XAMPP (and you already know not an ideal setup) ... but ... for the sake of exercise ... will begin ...

How much memory was allocated?  How much of that memory is being used by: Apache?  by MySQL?
Version of Moodle? Versions of Apache, MySQL, PHP. Can you locate error logs?  Share clips of those logs around the time/date your entity experienced the issues.  (that request says 'clips' ... not entire log files).

For the mysql config, logged onto the client:
mysql> show variables like '%max%';

That should be enough to start the disussion/cussion, me thinks!  Consider this a response from Ghost 1!

'spirit of sharing', Ken

That must make me the second ghost.

As you say XAMPP isn't recommended for production use and here's one of the reasons: XAMPP's builds of Apache and PHP have always been 32-bit (64-bit builds were issued for the first time this week!). So regardless of the RAM added, only 4 GB could ever be used by Moodle. The 32-bit build also prevents Moodle from performing file operations on files larger than 2 GB or handling values larger than 2^32 - 1 (e.g. from the database). This could contribute to issues over time as the amount and size of files grows over time, and the number of rows in the database increases.

You don't say what version of Moodle is in use but this could be an older version too?

One thing you could check is that the site cron is running, if it's not you'll see a message on Site administration → Notifications.

You could look into moving to a 64-bit XAMPP build. You'll need to check that your version of Moodle works with the PHP version in the XAMPP release you download. I strongly recommend you do a test migration first to make sure everything works before trying it with the live site.

Generally if you run Moodle on Microsoft Windows I strongly recommend using IIS instead of XAMPP/Apache if that's a way forward for you.

Michael, you've got one thing right, XAMPP is not for production, XAMPP is usually used when base operating system doesnt comes with a web server of its own (Windows Home editions) so developers can use XAMPP to develop web applications.

anyway, now you have to dig in history, 150 concurrent users isnt very resource demanding but there are plenty of factors playing the role to degrade the service overtime. so you have to find out, what was the initial moodle version installed? as it must have been upgraded overtime and every major moodle update comes with added features at the cost of hardware resource.

secondly, was the test questions remained the same throughout? as they must be changed on yearly, semi-annually basis, this adds to the calls to database.

thirdly, what kind of VM is your Windows server hosted on? as VM's (unless a true hypervisor is used) adds a layer of host operating system beneath, this adds to latency, therefore a direct hardware install is always better than a VM.

Leon already have mentioned 32-Bit, and its limitations of using RAM (3.5GB it is), but have you as well tried allocating more RAM resources to your DB? rather than just allocating to VM?

Lastly, using IIS would be best option, as you will be able to run same tests on same hardware, as sometime ago I had this scenario came up where moodle was setup on XAMPP and though was working, but very slow, so I switched it to IIS on weekend night, and first mail I was sent by the teacher in morning was from student saying what a speed difference, and its been 2 years, no complaints of speed or system getting down ever since.

my advice, switch to IIS and things will improve very very likely.