You didn't give much details about your setup.
- What version of Moodle? Is it the original version 2.5 years ago, or did you upgrade? How?
- Plattform and all the other software components: operating system, web-server, PHP (cache if there's one), database server? with version numbers.
- hardware of course! CPU, RAM, disk system (IDE, (S)ATA, RAID, ...).
- Network, connectivity (bandwidth, firewalls, ...)
- Is this a physical machine or a virtual machine? You mention a vendor. So it must be hosted. What is the guranteed performance?
- Did you (or your vendor) do any tuning? How?
People here need those parameters to judge whether the there is something unusual or not.