Users experienced performance issue, whether it is clicking menus, or saving records, the page just keeps on loading.

I already did:

Enabled Multi-Processor support for Odoo

PG tune wizard

Server Specifications:

Server specs Processor: Intel Xeon Processor E3-1240v3 (8MB Cache, 3.40 GHz) 4-Core

Motherboard: Intel Server Board S1200V3RPS (Rainbow Pass)

Memory: 4 x 8GB 1600MHz DDR3L ECC CL11 DIMM 1.35V

Hard Drive: 2 x 3.5in. 2TB 7200RPM 6Gb/s SATA Enterprise drive

RAID: R1

Number of simultaneous users: 15 - 20

Database size: 30.5MB

The Odoo instance has been up since October last year and the issue started only last week. Thanks