If it’s old uninsulated overheads then they’re very likely to be 16mm², possibly smaller…!
They are a hangover from the original “électrification rurale” at which time the grid demands now present were entirely unforeseen.
I once watched half a village get an entirely new high tension supply & new local low voltage cabling run in due to my client creating a new all electric house which ENEDIS happily agreed to supply, only to find that it was the last straw in that locality, with their 24/7 test reader showing long periods of only 165V P-N.