15. (3 points) There are three different sizes of cubic wooden blocks, A, B, and C, where the edge length of A is $\frac{1}{2}$ of the edge length of B, and the edge length of B is $\frac{2}{3}$ of the edge length of C. If A, B, and C blocks are used to form a large cube with the smallest possible volume (using at least one of each type). Then the minimum number of these three types of blocks needed is $\qquad$ blocks.
15. (3 points) There are three different sizes of cubic wooden blocks, A, B, and C, where the edge length of A is $\frac{1}{2}$ of the edge length of B, and the edge length of B is $\frac{2}{3}$ of the edge length of C. If A, B, and C blocks are used to form a large cube with the smallest possible volume (using at least one of each type). Then the minimum number of these three types of blocks needed is 50 _blocks.

【Solution】Let the edge length of A be 1, then the edge length of B is 2, and the edge length of C is 3,
So the volume of A $=1 \times 1 \times 1=1$;
The volume of B $=2 \times 2 \times 2=8$;
The volume of C $=3 \times 3 \times 3=27$;
According to the problem, the smallest edge length of the large cube formed is: $3+2=5$,
Then the smallest volume of the large cube is: $5 \times 5 \times 5=125$,
Based on the analysis and practical operation, when one C block is used, the maximum number of B blocks used is 7,
$$
\begin{array}{l}
125-3 \times 3 \times 3-2 \times 2 \times 2 \times 7, \\
=125-27-56, \\
=42,
\end{array}
$$

So 42 A blocks are needed,
$$
42+1+7=50 \text { (blocks), }
$$

Answer: The minimum number of these three types of blocks needed is 50 blocks.
Therefore, the answer is: 50.