how to fix a stuttering camera pan movement?
I think the Adobe article you linked to spells it out pretty well, especially with respect to the "7 second rule". I think you're just panning too fast.

Fast pans don't like sharp lines that run counter to the pan's motion. If you absolutely must pan at that speed, you'll need to reduce detail (ie, contrasty edges) during the fast pans.

So for starters, I think you need a lot of motion blur. I wouldn't start by using an effect to create motion blur, though. Instead, try using AE's built-in motion blur. Assuming you're in the comp that has the motion keyframes, turn on the motion blur switch for your Painting layer (the little balls icon):



..and then enable motion blur globally using its global toggle button:



Now you can adjust the shutter angle, samples, etc by going to the Advanced tab of the Composition Settings. Set the shutter to the max value 720 just to see if it helps. Lower the value until the judder begins to return.

Adding some grain may help imperceptibly reduce some detail, too. (You can simply create a 50% gray solid, add the Add Grain effect, and set the transfer mode to Overlay.) Play with intensity and size, and monochromatic vs color grain, to see what feels best.

Lastly, I don't think CC Force Motion Blur is a good choice in this case. If the built-in motion blur described above still isn't 'smeary' enough to get rid of sharp edges during pans, try Pixel Motion Blur instead, and set the shutter to something high like 1000 (just to see if it fixes the problem) and then lower the value until the judder begins to return.