Help with clownfish nem tank

[ponokareefer]

You'll want at least 10 * turnover in your 15 gallon. Make sure that your overflow or whatever it is you are planning on using can handle enough flow back through it to the sump.
The Mag 350, Eheim 1250, Tunze silence, or the KSP 5000 should all work to get that, and you could go with a little stronger pump than each of these if your overflow can handle it.