I routinely transplant plants as large as that one, the key i have found is being as gentle as possible when removing the plant from the old pot, the one in the picture is ideal because the bottom os much smaller than the top, that taper can mean all the difference. i would not hesitate to repot that plant, now, if the plant is completely i n flower mode and has stopped bud growth i might not bother, but otherwise i would just go gently and try not to shock the plant any more than you have to. some of the pots i use have bottoms that come off, and i will just set the one pot onto another and let the roots grow down into the fresh soil. givng the roots fresh soil to feed off of is always a good thing.
Cloth is the way to go. As big as you can manage without winding up in the hospital or at the chiropractor. 20 is probably getting pretty heavy.Don’t know if they make 15s. Then you have the expense of more soil also. Fear not the transplant!
Chasing the sun around all day must be a real hassle! No place out in the yard that you can put it in full sun? I would consider pistols this early kind of ominous also. But that could be because of where you live or chasing the sun. Maybe you will have a nice long pre-flower.