Oh dear. To respond to some of the above.
First, I did speak to the correct size & regardless of driving style, untoward events can happen. OBVIOUSLY, driving in an aware way vastly increases one's chances of not being caught out by events but, even so, & OBVIOUSLY, one still can be, And if they happen on wet bitumen, then compound does matter & tyre age does apart compound condition. Hence my recommendation of importation in the original size & another size for access to better wet tyres.
No I don't drive a DS but when the topic came up in another thread some time ago, some other correspondents reported satisfaction with non-standard sizes (including 195/65). Whether some undergearing matters or not is a matter of priorities. Considering non-standard sizes given the limited availability & expense of stuff in 185-15 is a legitimate option. If one's major priority is not having the tyre ripped to shreds on unsealed potholed roads, then commercial tyres in some non-standard but close enough size seems the best bet.
I repeat my offer that, were anyone to wish to have a copy of a relevant classic tyre test then AF-email me. The results for the Nankang Retro are daunting & an objective test is, I suggest, a useful offering that goes beyond anecdotal reports.