Front hub conversion Shimano HB-M756L XT to Thru-axle Has anybody converted a Shimano HB-M756L XT Front to a 15mm thru axle?

The problem is that my bike fork has 15mm holes for thru axle but I have a new/nice set of QR wheels. I need to either convert the hub (change the bearings and etc) to a 15mm and use my original thru axle or use two spacers in the fork holes in order to fit them and use QR.
Not possible. Convertible hubs are made to be that way, and no Shimano hubs are. There are no generic adapters or spacers that can do this.

756 XT far predates 15mm. There's no room for a 15mm axle in there.