I don't know, maybe he fits better as the older Muad'dib a few years later on. But pretty much every movie had the problem that Paul just looks much older than 15.
It's probably too much hassle for them to find two actors in the approopriate age categories that look somewhat similar to each other to sell that they are the same young person a few years later on.
Ein Ausschnitt des Bildes ist auch auf dem Cover von meiner uralten Ausgabe des Gottkaisers:
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Später im Buch ist auch nochmal ein größerer Ausschnitt zu sehen:
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