Yes, the scherzo is slower than usual. But Zinman doesn't drag the contrasting, mixed meter Trio sections either. Therefore, tempi are a bit more unified in the scherzo movement than usual. However, no sense of monotony sets in either - well, for me, anyway - because Zinman doesn't try to tame or tone-down Mahler's spooky and deliberate sound effects. In fact, they're done a bit better than usual.
If this scherzo had followed the first movement, I'd have more of a problem with its slower-than-usual tempo. But here, it's placed third, and the Andante Moderato movement is quicker than usual, clocking in well less than 15 minutes. It's a game plan that works well for me. I think Zinman's finale is terrific, and that's the main thing, I suppose.
Listen, I'm not suggesting that everybody run out and buy Zinman's Mahler 6, especially if you already own a few that you're happy with. But I'm very much a Mahler 6 nutcase, and this Zinman one has crept up to the top of my list. That doesn't mean that I'd want to throw the rest of them into the recycle pile either. If it weren't for the excellent sound and excellent playing, I'd probably cut the Eschenbach out of my collection. I'm just not a fan out dragging the slow movement out to 17, 18, or 19 minutes. But Philly plays fabulously, and the Ondine sound is excellent.
Hope this helps.
Barry