Hi guys, thanks for all the reply. I will try to modify the adjustment circuit later. I'm waiting for the replacement of lm 337. So i decided to install Im 7915 that lying arround on my workshop. I bypass the adjustment network so i goes straight to the center point and i decided to try it with the current booster and it works just fine. I got -13.8 V , about 1,2 V drop from -15 V after the output pair transistor. Below i attach some footage of the project. I hope when the replacement come, it will work as an adjustable one.