Yes. Unfortunately, you are grossly overstocked.
To make matters worse, the environment is not proper for some of the stock. I really, really encourage you to return the fish and inverts, then study up a little before you buy anything more AFTER the tanks are cycled.
First, fiddler crabs are not freshwater at all. Fish stores often sell them as aquatic freshwater inverts, but they are actually brackish and semiterrestrial. They are brackish and require a fair amount of salt in the water to maintain health. If they survive the cycyling process, which is doubtful, they will die within a month or two if kept in freshwater. Also, they require a habitat that allows them to completely leave the water at times.
Lemon tetras are a schooling fish. They should be kept in groups of six or more and require a large swimming area, 10 gallons minimum.
Guppys also require a larger swimming area than either a 1.5 or 3 gallon can supply.
I'd take all these critters back and see what you can humanely house in small aquariums.
For the three gallon, a male betta is a popular choice. They come in a wide variety of colors and have a great deal of personality. You can only keep one at time, but they are a very interactive pet.
For the 1.5, red cherry shrimp, maybe some amano shrimp are about all that will thrive in such a small tank. Except for limitations on fish, you can do a lot with a small tank like that, especially if you plant it with lowlight plants.
Like I said, I have both sizes that you have, and they can be excellent tanks.