OMITS 2015 Happy 2015!

This solution is very very very long....May be, somebody will give other solution.

Let us write $2015!$ on format like below:

$2015!\\=\color{#D61F06}{\left(5\times{10}\times{15}\times{20}\ldots\times{2010}\times{2015}\right)}\times\\{\left(1\times{2}\times{3}\times{4}\right)}\times{\left(6\times{7}\times{8}\times{9}\right)}\times{\ldots\times{\left(2011\times{2012}\times{2013}\times{2014}\right)}}\\=\color{#D61F06}{\left({5}^{403}\times{403!}\right)}\times\\{\left(1\times{2}\times{3}\times{4}\right)}\times{\left(6\times{7}\times{8}\times{9}\right)}\times{\ldots\times{\left(2011\times{2012}\times{2013}\times{2014}\right)}}\\=\color{#D61F06}{\left({10}^{403}\times{403!}\right)}\times{2^{-403}}\times\\{\left(1\times{2}\times{3}\times{4}\right)}\times{\left(6\times{7}\times{8}\times{9}\right)}\times{\ldots\times{\left(2011\times{2012}\times{2013}\times{2014}\right)}}$ .

Let us observe all product of each black item in the bracket. We can see that all last three digits of the product is $24$ . So, we can say that the last three digits of

$\begin{array}{c}&\dfrac{2015!}{{10}^{403}}&\equiv\color{#D61F06}{\left(403!\right)}\times{2^{-403}}\underbrace{\left(\times{24}\times{24}\times{24}\ldots\times{24}\right)}_\text{403 times}\\&\equiv\color{#D61F06}{\left(403!\right)}\underbrace{\left(\times{12}\times{12}\times{12}\ldots\times{12}\right)}_\text{403 times}\equiv\color{#D61F06}{\left(403!\right)}\times{{12}^{403}}\pmod{1000}\end{array}$

Using same method above, we will determine the last three digits non zero of $\color{#D61F06}{\left(403!\right)}$ .

$\begin{array}{c}&\dfrac{403!}{{10}^{80}}&\equiv\color{#D61F06}{\left(80!\right)}\times\left({403}\times{402}\times{401}\right)\times{{12}^{80}}\\&\equiv\color{#D61F06}{\left(80!\right)}\times{406}\times{{12}^{80}}\pmod{1000}\end{array}$

And for $~\color{#D61F06}{80!}$

$\dfrac{80!}{{10}^{16}}\equiv\color{#D61F06}{\left(16!\right)}\times{{12}^{16}}\pmod{1000}$

And the last for $~\color{#D61F06}{16!}$

$\dfrac{16!}{{10}^{3}}\equiv\color{#D61F06}{\left(3!\right)}\times{16}\times{{12}^{3}}\equiv96\times{{12}^{3}}\pmod{1000}$ .

Finally, we have

$\begin{array}{c}&\dfrac{2015!}{{10}^{403}}&\equiv{12}^{(403+80+16+3)}\times{406}\times{96}\equiv{12}^{502}\times976\\&\equiv{4^{502}}\times{3^{502}}\times{976}\pmod{1000}\end{array}$ .

For simplicity, we will work with modulo $8$ and $125$ to use Euler's theorem. Now we have:

$4^{502}\equiv\begin{cases}{16}^{251}\equiv0\pmod{8}\\\left(4^{\phi(125)}\right)^{5}\times{4^{2}}\equiv16\pmod{125}\end{cases}$

and $~~3^{502}\equiv\begin{cases}9^{251}\equiv1\pmod{8}\\\left(3^{\phi(125)}\right)^{5}\times{3^{2}}\equiv9\pmod{125}\end{cases}$

Note that $\phi(125)=\left(1-\dfrac{1}{5}\right)\times{125}=100$

By using Chinese Reminder Theorem we shall get that $4^{502}\equiv16\pmod{1000}~~$ and $~~3^{502}\equiv9\pmod{1000}$

Hence,

$\begin{array}{c}&\dfrac{2015!}{{10}^{403}}&\equiv{4}^{502}\times{3^{502}}\times{976}\equiv16\times{9}\times{976}\equiv140544\\&\equiv\boxed{\boxed{\boxed{\huge{544}}}}\pmod{1000}\end{array}$ .