Here we have a simple example
Clear["Global`*"];
col = {Green, Blue, Red, Purple};
lab = {"Label 1", "Label 2", "Lable 3", "Label 4"};
leg = PointLegend[col, lab, LegendMarkers -> {Style[●, 12]}, LabelStyle -> {FontFamily -> "Helvetica", 17}]
Is there a way to reduce the vertical distance between the labels?