Hello.

I have spend 15 k to go in moon, i've lost, i spawned in mossdeep poke center...

 

And NPC said I have to spend 15 k again. Is that a bug ? I cant spend so much money each time I lose, and i'm goona lose a lot of time, cause deoxys's fight skill ( one-shot ) has 70% accuracy

Some tactics is a pokemon with sturdy and use thunderwave to paralyze it first and cut its speed (magnemite).

Or a dark type counter move like Sucker Punch from physical poke like Absol or Kecleon should take it out easy.

Or else use a poke with Flash to lower its accuracy (gardevoir). A high lvl gardevoir should be able to withstand one hit.

Make sure you use revives mid battle too. Don't lose good luck.