"When I looked at the train tickets"
You can't mean at actual train tickets. If you are arriving in Frankfurt on an ICE, there are only the stations at the airport (Flughafen Fern) and the Hauptbahnhof. No other stops, and I can't find any station in Frankfurt am Main called "Frankfurt Ober".
You must have been looking at some ticketing website (not the Bahn or RailEurope).
If I put Frankfurt Hbf to Frankfurt, Oeserstrasse (Öserstrasse)180 on the RMV website, it gives me 23-25 minute connections, the shortest of which is every half hour, by S-Bahn (S1) 6 minutes to Frankfurt Nied Bahnhof, then eight minutes later via bus 59 6 minutes to Frankfurt Neufeld bus stop, then a 3 minute, 205 m walk to the hotel.
The trip from the hotel to the Messe (24 min) uses a bus, streetcar, then an S-Bahn.
The Messe is actually 4 minutes from the Hbf on a route taken by S1 - S5.
Here is the commuter train (S-/U-Bahn) map of Frankfurt.