I live in Germany and none of the engineers I know buy engine oil from Wurth and I have never seen it for sale here. Wurth are a very big company, but they seem to be mainly export orientated and if you want to use a top quality engine oil from Germany, I would recommend Liqui Moly (Lubro in the USA), which is the most popular engine oil company in Germany and overtook Castrol in sales figures this year. Fuchs is also thought to be a good company, but they don't compare to LM in production or product range terms.
The Germans produce some very good lubrication products and were the first folks to develop fully synthetic engine oils. German cars are driven very hard on the autobahn and the manufacturers recommend long service intervals, so most folks buying oil here tend to buy top quality products only, which is why Liqui Moly and Castrol dominate the local market.
No one except a long distance truck driver uses 15/40 as it causes more wear on initial start, particularly if it is cold, a 5/40 is probably the best viscosity range unless the manufacturer indicates otherwise.