PPI 2150 amp and 2 JL15W6

I was wondering how do you think 2 Jl15w6's chrome series would sound hooked up to my PPI 2150 600watt RMS would sound. this amp is only 4 ohm stable bridged so i would have to run it at 6 ohms.
I have this amp hooked up to my kenwood kfc-w3025's at 4 ohm but it is too powerful.
Also how should i make the box    sealed, port bandpass...etc and what cubic foot.

You should be able to go to www.jlaudio.com and get the information on how to build a box for these speakers. If they don't have the info on line you can call them by phone and they will talk to you about what you want to do as far as box building. They helped me before. I believe that these speakers are dual voice coil subs. You could wire your voice (if you have dual 4 ohm voice coils) coils in a series making each sub 8 ohms then wire your amp to them parallel giving the amp a 4 ohm load. This should give you 300 watts per speaker if the specs on your amp are as you say. You probabley would be underpowering them with only 300 per speaker. I would build a ported box for these because ported boxes use less power and work better with under powered subs. If you intend to build your own box you need to find the tuning frequency for these subs from JL as well. The 12 volt has a port length calculator to give you the tuning frequency of your box and port length, very helpful.      

Actually I think these subs are duel 6 ohm. so I am gonna have to run it 6 ohm bridged. I cant wait till i get them but im still wondering should i mount them cone up or down and i probally should build a nice size box since I listen to songs with lots of bass, like rap and techno.

If you run it at 6 ohms you will be sending less than 300 watts a peice, a lot less. I would venture to say it would sound pretty poor. You have some really nice equipment but when you hook it up and expect the trunk to blow open and it doesn't it is heartbreaking. I have been there. I would sell the amp and invest into at least an amp that runs 1000 watts rms, or trade the subs for dual 4 ohm vc subs. I use the older soundstream amps with much success and they are stable to .5 ohm mono. I am talking about the reference or rubicon class A series amps. They will slam. Their new stuff sucks. You probabley could sell your amp and pick up a different one on ebay. Best if it was 1 ohm stable mono which is hard to find. You could wire your subs in a series both at 3 ohms and wire your amp in a series which will give your amp a 1.5 ohm load.   Then you would have it running a good load but not making it so hot you can light a cigar off it. It also gives you better sound quality not to push an amp to its limit. Good luck with all else, any other questions let me know.