uhh, as your fish get bigger your gonna notice the matience on that tank is pure hell.
i had 22 in my 55 and got rid of 7. at the time i was running 2x 350b penguin filters(rated for 75 gallons). 15 is good and most are full grown if not close to it with a few 2" growing fastly. i have mbuna, 1 peacock, 2 tropheus and a syno eruptus and filted by 2 rena xp3's
if your going to keep them all make sure your doing decent water changes and have a filter that can handle it!
most some pics id love to see it