Target & Max Bit Rate - A Little confusing Need file to be 15 GB Blu-Ray Help????

I have a 2 and a half hour project on PPro CS 5.5 that I want to encode in H.264 Blu-Ray.  I want to get it to 15 GB.

What woud be the best settings to do so?

The Target Bit Rate and Max Bit Rate have a lot to do with it, but I am a little confused on what each of them really do. 

I just want to get it to 15 GB and make sure the Estimated file size somewhat accurate.

Is 15 GB too big for a Blu-Ray?

Thanks in advance

PPro CS 5.5

Media Encoder 5.5.

Thanks in advance