An R-15 cannot use SWM. If you want to stick with the SD receiver you would need the R-16 which is SWM compatible.
If you stay with the R series (there is an R22 but I don't know anything about it) you will not have to pay the DirecTV $10/month charge for HD which you would if you bought a new H series receiver even though you will not be receiving the HD signal.
I stuck out SD for as long as possible but went to HD kicking and screaming due to the awesome Genie receiver and the Trav'ler antenna. Even then I beat DirevTV up to give me the HD free for a year and the DVR fee free for 6 months.