You definitely tamped off center, your tamper was tilted toward the portafilter handle.
Are you sure that was 14-15 grams, are you weighing the dose or just guessing. Based on how high your tamper sides were after you tamped, I would guess more like 17g in that basket. Provided the Cimbali double basket is the same as the Faema style double baskets.
I would fine up the grind a little more, say one click or more on the JR, dose a little less so the top edge of the tamper piston side is almost even with the basket top, and go lighter on the tamp. It is important to keep the tamp straight, dose the same, and tamp the same, then just adjust the grind for the correct extraction speed. Don't change too many things at one time, one thing at a time.
You can see me grind/dose/tamp etc... in the last post of the
Latte Art Challenge[d] thread. That was a 15g dose.