The Sigma 15-30mm is a nice lens. Sharp even wide-open. But there was a problem for me : glare at the wide-end when shooting with the sun in front (not directly into the sun).
This lens come with an integrated flower-shape hood and a two-parts lens cap (a cylinder and a flat cap). Keep the cylinder part over the hood 1) to give better protection for the lens front element and 2) to reduce lens glare.
I owned this lens for a while before selling it for a more compact and a bit lighter Tamron 17-35mm.