They definitely aren't excessively high, charging more at least for some of these categories would probably be a good idea as long as it doesn't negatively impact the demand you get too much for you.

I was asked to do a pencil portrait, and it will have 2 people in it. I quickly spout out, that I would charge $50, and they plan on taking it, while I was not thinking I would do that with one person, but 2 people is different and I should charge more. 

It might be a price from the past when paychecks were a lot smaller, but I think of it as an introduction back into drawing again. 

When you find people that want art, you set a good price to make it worth doing. For the work you put into it, I am sure you will not be able to get anything to make it worth doing with the $7. 

The main problem is, this website is an artist website. a few people pass through that are not artist, but not create an account to interact. Mostly artist do that, and they are more interested in improving than buying art. 

When I work with a program, I do what it does best, to go with the flow and not spend time making it do what it is not good at. All mediums are like that, like pencil and water colors needs the white of the paper to be the brighter areas in the art, and you avoid filling them in. This website is like that, because it has things it does best for artist, while most new artist try to sell their art to other artist, and wonder why nobody is buying. 

The forums are helpful, and when it comes down to getting attention around here, to spend less time doing art, or do very bad art so any artist feels they can help with advice. 

Personally, I always sell my art to local people, and sell art with programming online. I spend no time at all trying to get noticed. When I first came here I looked at what makes artist more noticed, and a DD works, but this is a closed community. Being popular here is only here. People all over the world are outside of this closed community. It might be open to everyone but it has a lot of artist and tons of images being uploaded all the time. A person could get looking around and not remember why they came. That makes it closed to the outside, like the inside of a black hole, nothing gets out unless the artist uploads to a lot of other places. 
 

To be honest, I think those prices are way too low.  You could be charging 2-3x that much easily.

Regardless, I don't think prices have anything to do with your commission volume.  I might be wrong, but chibis just aren't in that high of demand anymore.  You're catering to a market that's overflooded and dying.