An unlimited supply of 8-cent and 15-cent stamps is available. Some amounts of postage cannot be made up exactly, e.g., 7 cents, 29 cents. What is the largest unattainable amount, i.e., the amount, say $n$, of postage which is unattainable while all amounts larger than $n$ are attainable? (Justify your answer.)
1. **Identify the problem type**: The problem is about finding the largest unattainable amount using two given denominations of stamps. This is a classic problem that can be solved using the Chicken McNugget Theorem (also known as the Frobenius Coin Problem).

2. **State the Chicken McNugget Theorem**: The theorem states that for two coprime integers \(a\) and \(b\), the largest integer that cannot be expressed as a non-negative integer combination of \(a\) and \(b\) is given by:
   \[
   n = ab - a - b
   \]
   Here, \(a = 8\) and \(b = 15\).

3. **Verify that the numbers are coprime**: We need to check that 8 and 15 are coprime, i.e., their greatest common divisor (gcd) is 1.
   \[
   \gcd(8, 15) = 1
   \]
   Since 8 and 15 are coprime, we can apply the Chicken McNugget Theorem.

4. **Apply the theorem**: Using the theorem, we calculate the largest unattainable amount:
   \[
   n = 8 \cdot 15 - 8 - 15
   \]
   \[
   n = 120 - 8 - 15
   \]
   \[
   n = 120 - 23
   \]
   \[
   n = 97
   \]

5. **Conclusion**: The largest unattainable amount of postage using 8-cent and 15-cent stamps is 97 cents.

The final answer is \(\boxed{97}\)