Welcome to the forum!
The Canon EF-S 10-22mm is quite good. I am not afraid to pay the money for L lenses, but am quite satisfied with the 10-22mm on a 7D, for my evidentiary images at work, and my personal shooting. Except for the lack of weather-sealing, the 10-22mm is probably, realistically, as good as its L lens counterpart, anyway. (16-35mm 2.8L)
At the wide end of the focal range, however, this lens, as will any rectilinear lens this wide, will severely distort people who are near the edges! This effect is lessened at the longer end of the zoom range. (Rectilinear lenses have optical elements that attempt to limit distortion at the edges, if the camera is level.) This lens should not be purchased on the eve of a family gathering; there is a learning period. Renting/borrowing, before buying, might be a wise strategy. There are rental houses that will ship a lens to you.
The EF-S is Canon's cropped-frame-sensor equivalent of a 16-35mm lens on a 35mm format, "full-frame" camera. If you are reading a professional photographer's blog, and he or she mentions using a 16-35mm lens, either Canon or Nikon, it is likely that he/she is using a "full-frame" camera.
Notably, few wedding and event photographers seem to use a 16-35mm on their full-frame cameras, preferring the 24-70mm focal length range, which on your cropped senor camera is equivalent to the angle-of-view of 15-112mm, if my math is correct. Canon does not make a lens matching this focal range. The 16-35mm is more of a photojournalist's lens, with 10-22mm being the cropped-frame equivalent.
An ultra-wide lens requires that the camera be held quite level, to minimize distortion of vertical lines. The distortion can be used artistically, so it should not be seen as a negative!
The 10-22mm can, indeed, "take in" a whole room, if the shooter backs into a corner, and holds the camera quite level, in a direction that bisects the angle of that corner. This does not necessarily mean the image will be interesting, but it does help me to quickly document a room in a series of images, when I wish to start the series with an overall shot. People in the room, who are not near the camera, will appear to be very small, in such a shot. For an interesting composition, there should, normally, be a foreground subject.
Some shooters prefer to shoot with a Fisheye lens, which is very wide, and unlike a rectilinear lens, makes no attempt to correct distortion. The fisheye effect can then be removed in post-processing, or left as-is for the artistic effect.
I have no experience with the 15-85mm EF-S lens, so have nothing to say about it, positive or negative. People seem to post plenty of positive commentary on-line. Notably, 15mm on a cropped-frame camera, such as yours, is equivalent to the 24mm end of the 24-70mm lenses favored by event photographers using full-frame/35mm-format cameras.
I am no expert, and make no claim to being a "pro" photographer. I just tend to type quite a bit.
I do shoot evidentiary (crime scene) photos for professional purposes, with a pair of 7D cameras.