The load index for 205/60/16 tyres is 92, or 96 XL (extra load/reinforced ?). The load index for 205/55/16 is 91, or 94 XL. This equates to 630kg (92) vs 615kg (91) standard load rating per tyre, so I don't think there's any safety issue.
There will also be a difference in speedo reading of 3%, so at an indicated 60mph the car will be traveling 2mph slower than standard.
But, if you happen to have an accident, and the insurance assessor happens to notice non-OE sized tyres, there could be an issue.