Pentax 15mm F4 L is an Auto Focus (AF) Wideangle Prime lens with APS-C / DX max sensor coverage. When mounted on a APS-C / DX sensor camera, it will give you an FF equivalent focal range of 22.5mm. With a max aperture of f4 at 15mm, this is a moderately fast lens.
Pentax 15mm F4 L is not a weather sealed lens, so you have to be extra careful against rain and dust.