The Latin American Giant Observatory (LAGO) is a widespread cosmic ray observatory which uses water-Cherenkov Detectors (WCD) deployed in nine Latin American countries, being able to detect transient events or long term modulation effects simultaneously at places having different geomagnetic rigidity cut-offs and altitudes. In this work, results of studies on cosmic ray muon flux variations during the Forbush decrease of 22 June 2015 registered by the LAGO detector installed at the University of Campinas, Brazil, ${22^{o}49^{'}03^{"}S, 47^{o}04^{'}11^{"}W}$ at 650 m a.s.l., the TANCA detector, are presented. TANCA is a cylindrical polyethylene tank of 10 $m^2$ containing a sealed liner with a reflective inner surface. The liner contains 11400 liters of ultra-pure water. Cherenkov light produced by the passage of particles through the water is collected by three nine-inch-diameter photomultiplier tubes. The experimental setup and detector performance is also presented. The studies on Forbush decrease contain comparisons with neutron monitors and indices of Earth's magnetic activity.