4 goldfish- and a catfish?

ok so about 4 months ago i wanted to start a 15 gal freshwater aquarium so i did got everything i needed filter,heater,air pump ect and let it cycle for a month i was told to get a gold fish to help it cycle so i did from a local pet shop the person told it would do well ina 15 gallon so i got it it was a buck and cute. well a naighbor of mine whos got 3 kids seen my tank and told me she wanted a fish tank and some fish for her kids so she went out to wal-mart got a gl bowl and 3 fancy goldfish. and a cat fish she told me how pretty her new aquarium was with the fish in it (i personally didnt see it) and i congradulated her. well about 2 weeks later she asked me to come over she wanted help witrh it so i went. the bowl had no gravel and was filthy she told me it stunk and she was just going to dump it down the toilet fish and all! i told her i would take the fish. well the goldfish i got from the pet store is an Oranda i just found out and the gold fish she gave me were 3 calico colored one has googly eyes like a black moore the other has a skinny head and the last one has a rounded head like my Oranda. the cat fish has long whiskers and spots. is my 15 gallon going to be big enough? they are all small now but how big will they get? i couldnt just let her flush them i have had them 3 weeks in quarintine and they are looking alot better. if this is too small i would like to get a bigger tank but i cant get a bigger tank right now maybe not for a few months will they all be ok untill i can get somthing bigger? my boyfreind has a freind who gets 100-300 gallon sized tanks all the time cleans them up then re-sells them i could get one from him but it will be awile befoe i can get the money to buy one. what does everyone suggest? is a hundred gallon enough for all 4 fish?