Do you have any adapters allowing me to change my pair of standard Novatec MTB hubs in boost version 12x148mm and 15x110mm spacing? Currently I have them for 15x100mm and 12x135mm TA.
No, this is not possible to do with Novatec hubs. Your rear hub has O.L.D. 135mm (spacing) so in case your model is a convertible hub you can go for 12x142mm TA just by exchanging its current axle. But that is the max length you can achieve with adapters (axle +side cap).
If you’re after boost spec 12x148mm you need to get a new boost hub, there is no other option.
Basic info on boost hubs:
Thanks to the wider hub you can have wider flanges which improves spoke bracing angle. This allows building stronger and stiffer wheels.
Main difference between boost and standard hub is that flange spacing for boost was increased by 6mm compared to standard hub:
It is impossible to make an adapter for standard hub that would shift the flanges from each other by 6mm so that is actually the reason why you cannot convert standard hub into boost version.
Same principle applies for front hub, where flange spacing was extended by 10mm:
You cannot use spacers to alter your current front hub 15x100 because brake rotor has its position also shifted.
It’s logical that turning a boost into standard hub is not possible neither, for the same reasons explained above.