Let's don't use molar mass
The equation is given by
[tex]\\ \sf\longmapsto C+2H_2\longrightarrow CH_4[/tex]
Let x moles of Hydrogen required to produce 15moles of methane
[tex]\\ \sf\longmapsto \dfrac{2}{1}=\dfrac{x}{15}[/tex]
[tex]\\ \sf\longmapsto x=15(3)[/tex]
[tex]\\ \sf\longmapsto x=45mol[/tex]