Kinda silly that that’s the only differences. You’d expect better maximum hardware specs for the Librem 15. Otherwise what’s really the point of having both a Librem 13 and 15? May as well just pick one and stop manufacturing the other. Kind-of a waste of resources to manufacture two different models if they’re pretty much identical anyway.
I’d still buy the 15 though - bigger screen (and I’m accustomed to a 17" screen, so 13 would be wayyy too tiny for me) and probably better ventilation than the 13. Smaller usually means worse heat dispersal.