Here's the thing. You can't fit four 15s in that trunk, not while giving them the proper airspace. You would need to rip out the back seat and build a wall to fit that many woofers. You'd be hard pressed to get even one beefy 15 in the correct enclosure in that trunk and still maintain any usable trunk space.
And then there's the cost of doing this properly. You're looking at probably $3-4,000 in amplifiers, probably $1000 in subwoofers, probably $400 in batteries, $300-800 for a high-output alternator or two, lots and lots of wire, and the cost of all of the labor to build your wall. Then you'll need to upgrade your car's suspension to support all of the added weight. You're basically looking at investing 4-5 times what your car is worth in the system.
My suggestion would be to just do 2 big 12s or one beefy 15 in a custom ported enclosure (there are plenty of vendors on here that can take your trunk measurements, listening preferences, and equipment into consideration and build you a custom box). Go with around 1500w, and that will bang harder than just about anything you'll encounter out in the real world. With that much power, you can probably get away with upgrading your stock battery and doing a big 3 wire upgrade.