I know about convicts being unsellable...I've seen those stock tanks at the local LFS!
I think i'm gonna try and breed rams or angelfish?
So take your pick...Rams or angels?
Probably the better choice. Also angels don't tend to be the best parents, and they'll often lay eggs right on the glass so removing the eggs isn't an option.
Go with bristlenose plecos, everyone loves them and you can easily house a pair in your 15g. Once they lay just remove the female and the male takes care of the babies. Then just add zucchini and leafy greens for the fry to much on. Also, you could put the female into your community tank while the male raises the young.