So much concern with people running under sized tires for safety, yet others here have had no issues with going a size larger tire for economy or larger size rim for looks.
Compared a 2010 Mk5 jetta DSG diesel 3330# to a 2012 Passat 3360#
WOW THATS HUGE!!! OMG EVERYONE CHECK THEIR LOAD RATING OF THEIR TIRES EVERYEONE DIES IF THEY RUN SMALLED DEATH TIRES ON THE PASSAT!!!!
Yeah sure the Mk6 jetta is lighter, but its only 3210#.
The \Passat is much larger but they stripped so much out of the car to get the size, but not the "density" of older VWs.
I say to the OP, biggest concern is where they place those wheel weights on the rim, I imagine these are Biolines. If not placed correctly they will drag on the caliper and rip the weight off, found out first hand when i tried to make an old jetta bioline a fullsize spare for the wife, didn't make it more than 5 feet before I found the problem.
As for the undersized tire, go for it, you won't kill anyone cause it's rolling a few more times a mile. I ran 205-60-16 on the old Jetta for 40K no issues.
The difference between stock Passat 16" 215-60-16 and 205-55-16 isn't night and day, the speedometer will be high and if you calculate MPG, it'll be a bit high.
Also the weight savings of the "16 rim tire combo and narrower contact patch may actually help your actual mpg over the bloated "18 rims.