12.5 kg on two stands (one at each end) is less than 15 lbs for each support when the weight is spread out between the support stands of a backdrop support like mine. That's pushing it, but I think it can handle it. I've got some 5 lb weights and will try hanging three off each of my poles.
I just tried this, and they will support the weight, but the clamps that lock the telescoping sections at height must be very tight or they will slip under the 15 lbs of load. Although knob tightened, they are just plastic. My test indicates that they will hold the weight of your backdrop, but if set up and taken down often, I feel that these clamps will be the first parts to fail. If I was going to use these stands to support that kind of weight and it always needed to be at the same height, I would drill holes through the telescoping poles to insert pins just above the clamps, thereby locking the height with the pins sitting on the clamp and preventing the poles from telescope collapsing under the weight. If done correctly, the pins would be easily removeable, so the telescoping poles could be collapsed when needed.
Autopoles are very good and a very strong method, if your studio can handle them. Quite expensive though.
Charley