What you want to achieve is technically (and depending on how the game manages DRM, also legally) impossible. What a compression software does, in simple and short words, is substituting the repeated bits of data with a reference, creating a dictionary to keep track of such references while doing so. Whoever decompresses that file can read the dictionary back and return the data to its original state. The final size of the files decreases this way, but it doesn't work like a magic trick...getting from 15 to 1.5gigs is almost impossible, unless the source data was exceedingly unoptimized, and pretty often that data is already compressed, or unless you used absurd dictionary sizes, which would make it too hard to decompress.
A "certain compression software", in this case, is the most indicated, but the more you compress with it, the more power and memory your PC (or your friend/brother/parent/individual's) will need to decompress it.
With that said, you can't just send a copy of your game to someone else, and it's the same reason for why I didn't type out the name of the software above. He needs his own personal CD-KEY, unless the game allows for the same one to be activated multiple times (nowadays, that means "no game").
His only option would be, obviously, to pirate it, which would be illegal and which would prevent you, due to forum rules, to get any more help here.
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