No 15 gallons is far too small for angels and clown loaches and plecs. That is a horrifically stocked tank IMO.
Angelfish get to about 6-8 inches tall and equally as long, they are also a territorial fish and that size tank does not provide any of that. Also because of their height they need a tall tank otherwise they really are trapped in a box, which these in question are.
Clown loaches are again a big fish, slowgrowing but never the less big fish. They will work out at about 10 inches to a foot long each. They also need to be in large groups ideally but again because of size most people keep about 5 or 6 in a 6 foot tank.
Plecs again massive massive fish this will get too at least 10 inches despite the tank they are in they grow very fast and your auntie is going to be in a real mess in a few months.
In a tank that overstocked, I feel the angel did not die of being egg bound as in a tank that size they wont have been able to grow to the size needed to breed. Nor will they have felt they had enough territory to breed or safely raise a brood. Since they described them as being egg bound I am guessing the fish was bloated. If this is the case it is more likely to have been dropsy an internal parasite problem that could have been solved with some medicine.
Your aunties tank sounds like an LFS has advised her to keep these fish as they are typical fish that are sold to unsuitable tanks. The only fish that belong in a 15 gallon tank on that list are the neon tetras.
Unfortunately its a no to this and I think it would be a good idea to pass my advice to your auntie and try and get her to join the forum and we can try and help her as well
If you want to keep a fish that is similar to angelfish in behaviour, you could try having a look at cockatoo cichlids called Apistogramma Cacatuoides have a search of them and see what you think. Also look at Bolivian Rams and Redbreasted Acaras they are other dwarf cichlids that would do nicely in your 15 gallon tank with some small fish like neon tetras, rummy nose tetras or harlequin rasboras.
Hope thats helped and sorry about the negativity but its to help you and to try and avert a disaster of a tank that will ultimately end in fish death like that of your aunts
Wills
*also this thread belongs in either the new world section or the tropical discussion as Angels are new world cichlids from south america rather than south africa.