First off, welcome to the forum!
Secondly, I can see your stocking leading to disaster.
The bushy nose will grow too big for your 15 gallon. He needs a 25+ to do well.
The Cory is a schooling fish and needs a group of 6 cories to play with.
The betta will probably end up killing the guppies.
If you were to add any more fish it would have to be some Cory's. The Cory's are school fish and the higher the number the better. I think that the recommended Minimum is 6 but I'm not completely sure, sorry.
Hopefully someone else can help advise.
I have recently removed the betta and now is in its own 5 gallon but thought about placing back in the tank but I guess not now. the bushy nose is a baby right now about 1.5 inches so this is a temporary tank .
Fyi -And the betta grew up with guppy fry so they get along. The betta was 4 weeks old when I introduced it with the guppy fry. Now the betta is 8 months old!