For searching in the Verlustlisten you shouldn't use Ancestry’s incomplete version, but the complete and manually indexed version by Compgen - Verein für Computergenealogie: Verlustlisten Erster Weltkrieg (German), search form (Nachname = family name, vorname = given name, Ort = (birth) place; you should fill only the first ones if possible as the original list contains many errors when it comes to places and places changed their name).
It returns 93 entries on Josef Berg. We can't tell which one is your relative without the following information:
- When and where was he born?
- Did he die in the war, if yes, what documents/details are available?
The person you mentioned earlier did not die in 1914 or 1915. (Please note, that Verlust (= loss) includes POW, wounded soldiers, soldiers missing in action and dead soldiers.)
There are also 7 entries for WWI graves of soldiers named Josef Berg (http://www.volksbund.de/graebersuche.html), but without additional information it is impossible which might be your ancestor’s.
You provided the following details:
- Josef Berg, born March 7, 1863 in Karlsruhe.
There is no Josef Berg from Karlsruhe in the Verlustlisten. When the war started in 1914, he was already 51 years old. Men until the age of 45 were drafted in the Imperial Army. Landsturm, the last reserve, also used men until the age of 45. I highly doubt your ancestor served in WWI at all. Do you have any evidence for that?
Please see my answer on How to find information on German soldiers from World War I and World War II? for more options researching German world war participants.