  There has been growing interest in studying hexagonal boron nitride (hBN) for
quantum technologies. Here, we investigate nitrogen isotope effects on boron
vacancy (V$_\text{B}$) defects, one of the candidates for quantum sensors, in
$^{15}$N isotopically enriched hBN synthesized using a metathesis reaction. The
Raman shifts are scaled with the reduced mass, consistent with previous work on
boron isotope enrichment. We obtain nitrogen isotopic composition-dependent
magnetic resonance spectra of V$_\text{B}$ defects and determine the magnitude
of the hyperfine interaction parameter of $^{15}$N spin to be 64 MHz. Our
investigation provides a design policy for hBNs for quantum sensing.
