DiscretePlot3D[PDF[MultivariatePoissonDistribution[8,{2,3}],{x,y}],{x,0,15},{y,0,15},PlotMarkers->"Sphere",ExtentSize->{{0,0.75},{0,0.75}},PlotRange->All,ColorFunction->"Rainbow",PlotLabel->Row[{"μ = ",8}],ImageSize->Medium]