The breast of SD 1.5 checkpoints are known for being a bit fake or too perfect, specially if you try to create small or big breasts.

This LORA was trained only with the torso of the image, with natural breasts. There are small, medium and large breasts. There are some artifacts in the large breasts, so is convenient to lower a little the strength on large and very large breasts.

This model can be used by itself or with LORAs to add more realism to partial or full body images, but is best used as an detailer LORA, used with inpaint.

This is a comparison created with Realistic Vision. Notice how the model have problems to create breasts that are smaller that a medium/big size. The Lora allows to create all the gamma from small (and perky) to large, all being very natural.

The second comparison was created using epicphotogasm. It can be noticed how the big breasts have a nice fall, with a more natural nipple position.