slow and jerky Graphics in 12.1 compared to older version 9.0

Consider the following piece of code

Manipulate[ Graphics[ {{Gray, Line@Table[RandomReal[1.5 {-1, 1}, {2, 2}], {10000}]}, Dynamic[Disk[{0.1 a Cos[a], 0.12 Sin[a]}, 0.1]]}, PlotRange -> 1.5, FrameTicks -> False, Frame -> True], {a, 0, 4 \[Pi]}] 

Running the above code I find that the Graphics in newer versions of Mathematica (e.g. version 12.1) are jerky and are rendered considerably slower. I ran the same code in version 9.0 and it runs relatively smoothly.

Does someone know why this is so? and what changed between the older and the newer versions of Mathematica?