There is nothing wrong with the 2015's size and feel. It does not need to be lighter than that. Losing basics like an internal HDMI port and SD card slot are not acceptable for me as a media professional - period - for whatever tradeoff.
I don't want to have to dig some adapter out of my bag because the manufacturer of the laptops I've used for almost two decades has suddenly gone daft, prioritizing thinness over the device actually functioning, even as effectively as the previous units, that I have ardently supported for years (I still use an iMac G4 every day for cartoons and random drawings in Flash.)
Don't even get me started on the SSD/RAM being soldered to the Logic Board, either - I'm not even sure if other manufacturers are doing this, but to a girl who used to build her own towers from scratch, is not particularly wealthy, but also not particularly poor, and has counted on upgrading her devices for years to get value out of them when she can later afford it - this feels like an actual slap in the face.
I would personally never purchase a personal computer that I would e.g. do development on, that I could not remove the hard drive of myself, even if just for data recovery purposes.