Provided information:
The formula for compound interest with half-yearly compounding is:
\[ A = P \left(1 + \frac{r}{n} \right)^{nt} \]
Substituting the given values:
\[ 18522 = P \left(1 + \frac{0.10}{2} \right)^{2 \times 1.5} \] \[ 18522 = P (1.05)^3 \] \[ 18522 = P \times 1.157625 \]
Calculating the Principal (\( P \)):
\[ P = \frac{18522}{1.157625} \approx 16000 \]
Result: The principal amount initially invested was: \[ \boxed{16000} \]