Even if it is pV=nRT,
p=101,000 pa
V=1.5*10^-5 m^3
n=?
R=8.314
T=273+15=288 K
n=pV/RT
(101,000*(1.5*10^-5))/(8.314*288)= 6.327..... *10^-4 moles
15cm^3=15g assuming standard density.
Number of moles= 15/Mr
Something does not seem quite right or if my working out is wrong please tell me.