In all seriousness, it doesn't take an engineer to realize choking a 4 lane highway down to a 2 lane country road will slow transit and cause a bottle neck. This is true with vacuum, water, air, etc...
Carpet cleaners are smart crafty folks, take a fresh look at your whole system, the answers are staring you in the face.
Now to address the specific question, if you run 2" pipe out to a 1.5" wand there is some restriction, but not as bad as a 10' whip of 1.5" as it's the smaller diameter x the linear feet (ie:10-14') that causes frictional loss on the airstream. When in doubt go BIGGER you won't look back.
ps: who said 2" hose is heavy? less flexible maybe, but it's not really heavy, and you should know not ALL 2" hose is made the same, we spent 2 years getting the formula just right....If you ask HydraMaster nicely they just might bring some over.