Even Fuscus in a 15 will most likely be a problem unless you have a decent sized sump, refugium and skimmer.
The height of the tank isn't the problem in this case, it's the amount of water and the fact seahorse water degrades very fast.
Without the sump, refugium and skimmer, be sure to test for ammonia daily and be prepared to do major water changes frequently to keep the water from degrading.
You will probably have to vacuum uneaten food and detritus daily.