I have a bit over 30 gallons of water and the ice probe is barely able to move it. I wouldn't expect more than a couple of degrees with 15 gallons.
On it's own, the probe couldn't handle keeping my 30 gallons under control. A fan directed at the surface of the sump is actually more effective for me.
40 Gal Hex, 10 Gal Sump, CPR overflow with Mag 7 return, Maxxima 35 RO
, 10K MH
pendant, 2 x 15W actinic, 1 yellow tail damsel, 1 high fin goby, 40lbs LR
.com rock, 1 red head goby, 1 algae blenny, Leather, blastomussa, sun, and hammer corals, green polyps, carpet anemone, 2 sexy shrimp...and more LR
critters than you could imagine in your worst nightmares.... Mantis in 5 gal