[Jason Maner]

Use the activity monitor of your Mac OS X to evaluate the usage of memory, CPU and other resources. Must make sure to run this very utility and check it as well on regular intervals. You will know what is the virtual thing causing the slow performance of your system.

If nothing good comes out of it, you can try to reset system management Controller or the SMC: https://support.apple.com/kb/HT3964.
Besides, upgrade your RAM by adding additional memory to the Mac, uninstalling vague items which are not in use. Cleaning up browsing history, clear them, caches, cookies and the download history as well.

Reference: https://www.boostmacperformance.com