I would guess that to be true and I've wanted one for a while, but it seems that the S&W 15-22 runs about as much as one of these uppers. Hmmm....think I'll save my pennies for one of those, instead
Personally, I would recommend a CCMG dedicated .22LR upper on an AR-15 lower over an S&W 15-22. They are incredibly accurate and reliable, and I prefer the forged receiver and ability to use many standard AR parts to the plastic construction and proprietary parts of the S&W 15-22.
Yes - the whole setup is a little more expensive that an S&W 15-22 (which is a fine .22LR rifle in its own right), but if you build your own lower, the overall difference in cost is only about $150 or less.
Here is a link to my experience with my CMMG upper: