Building new system starting with power amp. What would you choose ?

Coda full class A amps are hard to beat.  

Again, depends on your speaker choice.

Respectfully,
Jose

Once again, the tail wants to wag the dog.

Engineering is all about achieving an optimal result within the constraints you have to work with.   Constraints are more than just budget, though that is the most obvious.  How big is your room?  What kind of music do you listen to?  How loud?  Decoration is an issue and of course, there's WAF to consider for many.

So starting with the power amp and going from there is a useless question.

That being said, with $15k to play with, I'd get a pair of VTA M125 monoblock tube amps at 120 watts each and look for a used pair of Avalon Eidolon loudspeakers.  With care you could do all of that for $15k.

Odyssey Audio Stratos Exstream mono blocks, Symphonic Line Kraft 300 dual mono Amp.

If you are a Tube kind of guy, then try the TriangleArt M100's just for the heck of it. I believe you will be amazed at what you will get from them.
Call and talk to Tom, he will set you up.

Because just starting out you have no idea what you really like. It will prob take years to grow, learn as evolve as you better understand what you like and what products offer what. 
Amp- I would start my buying used because if you don’t like you can resell for close to what you paid as you learn. Stick with top notch brands that hold their value.