A rare "Kastenzehner", an early series class 110 locomotive with the box-shaped front, in contrast to the more aerodynamic "Bügelfalte" cab style. Seen here at Cologne Central, pulling an InterCity replacement train from Bonn to Hamm.
This specimen was built in 1958 by Henschel, in continued service for over half a century by now! That's what I call well made and long lasting! Try finding a bus, ship or plane this old in the developed world that's still in use... Not as preserved unit for nostalgia runs, fueled by money from enthusiasts, but in proper service, even with a scrap-happy company like DB.
And yes, that gent to our right took a photo of it as well.
The 115 is just a re-numbered 110, to show that they're owned by DB AutoZug, rather than DB Regio. You can sometimes even see the residue of the 0 that had the 5 stuck on top of it.
I have a response to the question posed by your description: the former PRR GG1 electrics were in service with some operator from 1934 to 1983 -- I know that doesn't count as in use today, but it gives them close to the 50 year longevity described.