Calculators that say x fish for any particular tank should be avoided. The old guideline was 1 inch of adult sized fish per American gallon, ie per 3.75 litres. And that only applied to narrow bodies fish up to three inches long. By that rule, a 15 litre biorb can hold a max of 4 inches of fish, and a 55 litre tank 14.5 inches of fish. That's not the number of fish but the total size they grow to.
The fish in your list:
Congo tetras are quite big fish (males up to 8cm, females 6) and they are fast swimmers. They need a tank at least 48 inches/122cm long. They are also shoaling fish so you'd need more than 2 of them.
Dwarf gouramis would fit in a 55 litre tank. However, a lot of them are infected with dwarf gourami disease before they arrive in the country from farms in the far east, and they commonly die within a couple of months. A better choice for a 55 litre tank is the honey gourami. Some shops insist on calling them honey dwarf gouramis but dwarfs and honeys are two separate species.
You might get away with cardinals in a 55 litre tank, though they'd be better in a tank at least 60cm long.
Guppies would be fine in a 55 litre, preferably if you have hard water. But these fish have been very inbred making them quite weak fish. Keep only males; if you have males and females (which must be kept as at least 2 females for every male) you'd be knee deep in fry in next to no time.
Shrimps - fine in a 55 litre and the 15 litre biorb. Stick to one colour as blue and red are the same species and will interbreed giving you a tank of brown shrimp.
A 15 litre biorb is a very difficult tank to stock. Does it have a heater? If it does, it would make a good shrimp tank and with no fish to eat the baby shrimp you could have a nice colony of them in there.
For a 55-ish litre tank, there are quite a few small fish to choose from, depending on if your water is soft or hard - your water company's website should have that info somewhere. Although many fish will cope with water outside their preferred hardness, they will be happier in water nearer their preference.
I like
this website for checking a particular fish's water preferences and tank size. It has more entries than the fish profiles on here, and it gives more info. For a 60 cm long tank look at -
For soft water - ember tetras, chili rasboras, Microdevario.
For hard water - endlers (male only, they breed like rabbits as for guppies!),
emerald rasboras