The SD15 is an update of and replacement for the SD14, which was launched in 2007. It has the same body and most of the same features, including the same sensor, but there are a couple of improvements, including a larger higher resolution LCD monitor and a new faster processor.
The SD15 is a large and surprisingly heavy camera, and there's no denying that the body design looks a bit dated. It measures 144 x 107.3 x 80.5mm and weighs 680g minus the battery. The Canon EOS 550D measures 128.8 x 97.3 x 62mm and weighs 530g, while the Nikon D5000 is 127 x 104 x 80 and 560g; the Sigma does look and feel like a bit of a brick by comparison. The build quality is good though, and although the SD15 has a plastic body it feels sturdy and well made. The body shape is rather square and chunky but if you don't mind the weight it is quite easy to handle, and the large handgrip and sculpted rear thumb rest provide a comfortable and secure grip.
The control interface has been slightly altered from the SD14. It is fairly comprehensive, with single-function buttons for AF mode, metering mode and ISO setting clustered beside the thumb rest. Adjustments are made by rotating the bezel around the shutter button, but this is quite stiff and rather awkwardly positioned. Changes are displayed on the rather small and dim LCD display on the top panel, although you have to be looking almost straight down at it to see what's going on. Focus target selection is also shown in the viewfinder, but metering mode is not.
The camera has a function menu which also shows focus target selection, as well as allowing adjustment of flash mode and AF mode, but nothing else. There is also another Quick Menu which controls image size and quality, white balance and a limited range of colour settings.