I wouldn't want to do 15k miles a year in a 1.5Dci Megane, that's for sure.
Nice enough car if you do 6K or less a year, but beyond that they are a bit flimsy, road handling/noise isn't great and the 1.5 DCi engine will feel underpowered (assuming the 80BHP version).
I had the 1.9DCi 130 for 3 years and although little went wrong (needed a new clutch in year 2 @ 80k miles), I paid £3100 for it and got near enough that trade-in for it after 3 years. I also only did approx 7k miles a year in it (yes I know, doesn't warrant a diesel etc etc, I had my reasons).
Although the car did me well, I got it for a good price and really cannot recommend it for that kind of mileage, you want somewhere comfy and refined, the seats are flimsy and the cabin rattles, go for an older/less specced larger car imo.
to be honest your selling it to me here
i basically will be driving it to work on a sunday night, and back home again on friday night (130 miles each way) so if it has a little rattle or the seats are a bit flimsy its not the end of the world as during the week it'll just sit there.
i don't fly about, ~65mph usually so power isn't really an issue either, the main reason i'm after one is the fuel economy - and although you have said that a 2.0 passat (or other older cars) can achieve a good mpg i'd like to have as new a car as possible to try and avoid any problems in the future.
I've read that 4 year old / 72000 miles meganes will be needing a new cam belt. all need a good check for oil leaks and the tdc sensor. i think i can get hold of one and make a few minor repairs (if needed) for 5k.