I am baking a simulation which is taking up roughly 15 GB of memory, is this normal? I am baking full smoke simulation with high resolution and high definition.
Assuming you mean Hard drive space, not RAM, there is one thing you can do to reduce this:
You can set the Compression to Heavy in the Physics panel > Smoke Domain settings > Smoke cache:
Note that this will take more CPU usage, possibly slowing down the bake time.
Have a look at this thread on BA for more information and some comparisons.