If $L=\displaystyle \lim_{x \rightarrow 0} \frac{\sqrt{x^{2} + 2014^{2}}-2014}{\sqrt{x^2+2015^{2}}-2015}$, and $L$ can be represented in the form $\dfrac{a}{b}$, find $a-b$. Ensure that $a$ and $b$ are relatively prime.

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