Not sure where you got 15lbs, but that is a heavy estimate for a Sendero. I shoot the 300 Win Mag and have a Vortex Viper PST
6x24 on it, and it comes in at about 11lbs, maybe a little under. I swapped out the stock which shaved a half pound, maybe a little more. The gun is heavy yes, but I lug that thing with me on all my alpine hunts. It is worth it to me, especially if you are in areas that you are going to be presented with longer shots. If you go with the a Tikka, no doubt they are great guns, but with the 300wm round, be prepared to get your ass beat by that recoil. If it were me, and really wanted a light weight rifle, and liked Tikka's, im going with a 270.
As far as production rifles go, I love the Sendero. Like I mentioned above I swapped the HS stock for the McMillan Game Scout. Shave a little weight and doesnt have that massive palm swell and wide forend like the HS has. I shoot 180 gr soft tips, but that may change when/if I start hand loading.