the #15 head is a turbo head so at least the prechambers from any other turbo heads will fit the 15 mm bores but the difference between vertical and inclined would have to be addressed if that is what is available.

looking at the two pictures of his original injectors there is nothing in those pictures that would lead me to assume that it was inclined injection in that #15 head, there are no plastic rings that are originally installed in the inclined installations, and the part of the prechamber lock ring that can be seen doesn't look like the serrated/splined prechamber lock rings either. A good look/picture of the lock ring would help for sure.