Although I have no experience on either GT 15 or 16 I can pretty well tell you it will tire you just as soon , the high end slaloms regardless of brand are designed to turn 6 balls where the "crossover" skis , Senate & C , HO CX and CX SL , Connelly V and V carbon ride higher in the water and subsequently do not tire you as soon. FWIW I am 46 and am looking at a HO A2 ... yes I will tire quicker but the trade off for me is worth it , less sets but at higher performance. I think you are likely already on the right ski for you. If I could find a CX SL or Senate C I would be buying them. That being said , how much for your 2011 Senate C ? :)