: ...the valjoux 230 mainspring barrel does not
: have overwind protection, so wind it gently
: 'til the crown stops turning...then it's
: fully-wound.
===============

I agree with Walter. 1 time a day 24 hours. Like every AM. Not 2 times a day.

Now see if it still looses 15 sec. a day. If It does and or even more now that its fully wound.

Take it back and tell your watchmaker how you where it. ( left wrist and up/ on top or right wrist ect) Then tell him it looses time and to reregulate+
If you can post a photo of your fine watch.
Good luck
Peter