To be frank, between a 15'' and 16'' there will not be much of a difference in handling. If you extrapolate the differences out a few wheels sizes then you would definitely notice but between these two I wouldn't expect anything significant. As for the speedometer change, a proper -1 application (meaning going to 15's) should not affect anything because the 1'' loss in the wheel size would be negated by a 1'' growth in the tire height.
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