For a cone to fit perfectly inside the can it needs to have the same base circle size and same height.
Work out the height of the can first:
[tex]height = \frac{volume}{ \pi *radius^{2} } [/tex]
[tex]height = \frac{15}{ \pi *1^{2} } [/tex]
[tex]height = 4.77 [/tex]
This means your cone can have a max height of 4.77 and the same base circle (diameter of 2 / radius 1).
Work out the volume of cone:
[tex]Volume = \pi * radius^{2} * \frac{height}{3} [/tex]
[tex]Volume = \pi * 1^{2} * \frac{4.77}{3} [/tex]
[tex]Volume = 5 \pi * radius^{2} * \frac{height}{3} [/tex]
The volume of your cone which fits perfectly inside the can is 5.