Better work with anime models. Almost doesn't work with realistic.

Best weights:
0.8-1 for anime models.
1-1.1 for realistic(Not guaranteed).

Prompt:
You can use words: "breasts(small/large/huge), nipples, cupbi, wear cupbi" for better results.

Example:
detailed, best quality, masterpiece, 1girl, small breasts, <lora:cupbi15:0.8>, wear cupbi

Tested with:
Reliberate (Clip skip: 1) - Bad, or doesn't work.
Hassaku (Clip skip: 2)