I've rushed previous generations and I don't remember them being this fast.From what I've heard the streamer is rushing, skipping what they can.
14 hours seems about in-line with previous entries in that case.
Rushing and skipping while being 3 to 5 lvl over gym 7.
In HGSS, I defeated every trainer (fled every wild battle though) and my team of 6 was almost 10 lvl UNDER the first pokemon in Lance's team in the first league.
Generation 2 runs will always lead you to being underleveled without grinding, and they didn't change that in HGSS.