RotoLok refers to the piping connections at the compressor, not the compression mechanism itself. A RotoLok fitting functions a lot like a standard piping union. The xl15i has a scroll compressor with RotoLok fittings.
From an end user standpoint the RotoLok versus soldered joints makes no difference. When you are standing on top of a compressor inside a condensing unit, and your helper is pulling on a 24" pipe wrench with a 4 foot cheater bar on the end, trying to break the RotoLok loose, you will form your own opinions!
The XL15i uses a scroll compressor and the sound blanket is standard equipment. They are fairly quiet running but, as with most scrolls, they do make some start-up noise when they have been off for a while. The start-up noise lasts for about two seconds when the spirals make initial contact. After that they are much quieter than the old reciprocating compressors.