lower compatibility option for pgf plot

lecture.cls

@@ -28,7 +28,7 @@
 \RequirePackage{stackrel}
 
 \usetikzlibrary{quotes, angles}
-\pgfplotsset{compat=1.16} % or \pgfplotsset{compat=newest}
+\pgfplotsset{compat=1.15} % or \pgfplotsset{compat=newest}
 
 \geometry{
     bottom=35mm