You know which generation of L7 it is? Post a pic
That Onyx amp above is too much for it. The 1st/2nd gen L7s(black cone and the non-shiny silver/pewter cone) won't take more than 700 watts for too long as it has the tendency to rip the tinsel leads. I blew my 2nd-gen L7 with a HiFonics Brutus 1606D at about 3/4 volume - tinsel leads came off from the cone. The 3rd gen(shiny silver cone) I don't know but I know the same shiny coned L5 will also rip the tinsel leads(I had one and blew it with the same brutus 1606D). The latest-gen L7(black cone with small white L7 letter in the middle) is the one you want as it is redesigned and don't have any problems.
The latest-gen L7 looks like this and this is the one you want
NEW KICKER S15L7 15" L7 SUB CAR AUDIO 2000W SUBWOOFER | eBay
If you have the latest-gen L7 then bring on the Onyx, otherwise pick something that's just 2 ohm stable and makes 500~600 watts and call it safe and happy.