Not sure what that poster's geographic location has to do with whether or not a 15W-40 HDEO is suitable for an old Euro car.
Many Euro and Brit oldies speced a 20W-50 for warm weather conditions and many drivers of the older machines find a 15W-40 HDEO to be very suitable, particularly since these oils offer well over the 3.5 HTHS required by most more modern manufacturer's certs and they also feature low volatility, much lower than the Grp III 5W-40 HDEOs that some use instead.
I've used Delvac 1300 in my old BMW with good results, for example.
What I have to chuckle about is how you guys get hosed on motor oil.
Over here, Shell Rotella T4 would be the equivalent oil and it can be bought for $12/gal, which translates to around E11.40, or around E2.85/liter.
There are also current MIRs on Rotella, Delvac and Delo HDEOs ATM that make them even cheaper.
In any car that called for a PCMO 20W-50 or an A3/B3 forty grade, a 15W-40 HDEO would make a great deal of sense in terms of both performance and cost.
A straight SAE 30 or 40 might be a good alternative as well for warm weather use, since these grades offer both plenty high HTHS as well as very low volatility, although I don't know how available those grades are in Europe.
You can buy Shell Rotella SAE 30 all day every day at Walmarts here, and you'd also be able to get the MIR.