Yeah my bad the link I gave you for the clip light, are actually flora clip lights lol, again my bad. No you were sent the correct lighting for the tank.
Anyway, you could get 2 of the flora clip lights, and set them up on each side of the tank. It's what I do with my 2 Finnex clip lights on the 6 gallon edge, this way each side of the tank is getting the same amount of light.
And with the 2 clip lights you could also do a dry start method with dwarf baby tears, and some dwarf hair grass. You can google "dry start aquarium method" or you can seek the advice from the substrate forum as too what substrate works best for doing dry starts.
Now to the co2, you can certainly setup a co2 system for the tank, that's something left to your discretion. But if you do the dry start method with the dwarf baby tears & stuff, I would definitely go with a small co2 setup for the tank.
Plus plants respond better to actual co2, compared to a carbon based supplement like Excel.
15g Fluval Flex - Will be a planted shrimp tank