I am not a professional shooter by any means, but this is just my humble opinion on marskmanship and the two weapons in question. I did shoot competetively in NRA .22 contests in my teens using a Browning T-Bolt .22 and did quite well, winning many competitions and acquiring an impressive collection of trophies and awards and I also consistantly qualified as an expert marksman with the M16-A2 in the military and consider myself to be a "pretty good shot" for what it's worth.
I currently own the S&W 15-22 that I converted to a M4 / CAR style with open sights and have not used a scope on it as of yet. I have owned both the Ruger 10/22 Carbine and the Ruger 10/22 Sporter model with the walnut stock (the walnut Sporter stock is a little bit longer than the carbine stock and I believe adds a slight amount of accuracy, but that is proably just in my head because I just think the walnut sporter stock is nicer looking, lol). Other than changing the handguard on the 15-22 and adding a scope on the 10/22, both were "out of the box" with no other performance enhancements.
I have used both open sights and a $200 Nikon ProStaff 3-9x40 on the 10/22 and found for my purposes (casual target shooting and plinking cans and the odd potato or two) the 10/22 to be quite accurate. I could consistantly hit what I guess would be the size of a quarter (which I am happy with as a shot group) at around 50 feet with open sights and around 100-150 feet with the aforementioned scope.
With the 15-22 using open sights I seem to be able to hit the same quarter sized area at around 50 feet or so with what I consider the same shot consistency. By that I mean that I seem to get about the same amount of "strays" out of that quarter sized area, which I attribute to shooter error. I have not tried using a scope on the 15-22 yet, but I would assume that the accuracy would be about the same at the 100-150 feet range with the scope.
Now to be more specific about the last two paragraphs. Those quarter size shot groups were from the sitting position at a bench using a sandbag front rest to stabalize the weapon during sighting in at the outdoor range. That's the only time I use paper targets and actually gauge my shot groups for accuracy and size. After I get the weapon zeroed in, I usually don't go to the range. Living in Arizona we have lots of open desert which to go shooting in. We usually bring biodegradable clays, tin cans (yes, we police up after ourselves), or bags of potatoes which provide plenty of fun targets to shoot at. Also, I'd be plenty happy with either one for small game or varmint shooting if I was so inclined.
I sold my Ruger 10/22 Sporter after I bought the S&W 15-22 mainly because the 15-22 to me was just as accurate, easier to field strip and clean, has way more customizing possibilities and is just more of an all around "fun gun". I do like accuracy and even before I bought the 15-22 I planned on selling the 10/22 for a more accurate bolt action. I was planning on either another Ruger but was leaning more heavily towards the Browning.
So I guess the point of all my rambling, is..... 1.) Yes, out of the box the 15-22 can hang with the 10/22, and honestly, to me, the difference between the 10/22 and the 15-22 for the average shooter (me included) is negligible unless you have the thing clamped down in a bench vise and are splitting hairs..... so..... 2.) Pick the one you like best, considering its form and functionality for your purpose..... and..... 3.) If you want a really really accurate weapon, the best option IMO is bolt action all the way.
Hope that helped and after reading all I wrote, it appears I have way too much time on my hands, lol.
