Can I put a Salvini cichlid in a 15 gallon tank or a pair of breeding convicts or can i olny keep one convict.?

i already have the 15 gal cycled and the ph ammonia and nitrite is okay i have done all the tests using the mini master test kit im am really set on cichlids is it also okay if i feed the cichlids feeder fish because my friend fed his oscar feeder fish and it never got any diseases and hes been feeding it that for three years