Step 1: Find the total number of shirts.
The box contains
\[
6+4+2+3=15
\]
shirts.
Hence, the total number of ways of selecting \(2\) shirts is
\[
{}^{15}C_2
=
\frac{15\times 14}{2}
=
105.
\]
Step 2: Find the number of ways of selecting two white shirts.
There are \(2\) white shirts.
Therefore,
\[
{}^{2}C_2=1.
\]
Step 3: Find the number of ways of selecting two blue shirts.
There are \(3\) blue shirts.
Therefore,
\[
{}^{3}C_2
=
\frac{3\times 2}{2}
=
3.
\]
Step 4: Find the total favourable cases.
The events “both white” and “both blue” are mutually exclusive.
Hence,
\[
\text{Favourable cases}
=
1+3
=
4.
\]
Step 5: Calculate the probability.
\[
P
=
\frac{\text{Favourable cases}}
{\text{Total cases}}
=
\frac{4}{105}.
\]
Step 6: Final conclusion.
Therefore,
\[
\boxed{\frac{4}{105}}
\]