HF Propagation Widget
Many amateur radio websites present widgets that may assist radio hams in determining Global Propagation Conditions during the day and night. The data is based on SFI, SN, A, and K indices.
A banner showing global propagation conditions
banner courtesy of Paul L Herrman, N0NBH
This kind of banners ignore many factors, such as your location, the DX location, the characteristics of your station, and the DX station. Even if 15m is labeled as Poor, you will be able to hear something on the band. See a review of a similar widget showing global hf conditions.
The project "Understanding HF Propagation" provides a detailed overview and tutorials on HF propagation.