If there is a physical poster session, it can be organized in two different ways. First, they might give you the opportunity to have a two-minute talk. (Times might vary.) This means you have to give the "elevator pitch". Then you can see whether anyone wants to talk to you as you stand next to the poster.
Second, they just put up the posters along the walls and aisles of a big conference room. You stand next to the poster. Some people will come around and look at the poster. Some of these will want to talk to you. From my experience, you are better off with the equivalent of the "elevator pitch" as the attendees will have difficulties processing all the information in the room. Conferences are physically draining (long sessions, jet-lag, exhausted by travel, your body not being used to the schedule, ...) so your observers are not going to be in the best shape. I would even suggest to have a technical report handy in case someone is really interested. A URL to a technical report is also useful.
In your case, you are giving a talk so the poster is a bit superfluous.
Poster sessions have various reasons. Conference organizers might want them in order to attract more attendees. They can be useful for making contacts for recruiting. Occasionally, you have time to talk shop with someone working on something related. Sometimes poster sessions are limited, sometimes the posters are up during the whole conference suggesting that you should spend your breaks hanging out near your poster in order to talk shop in case somebody else wants to. In all cases, I do not see how a difficult to read poster is useful.
TLTR: From my experience, overloading a poster with content is not helpful. Especially not in your case as you are already giving the talk.
