Are my batteries too small?
 

I am currently running a 3s 4000 (waiting on a 2s 5000 to come in) in my hyper 7 pro . Im only getting like 15 min of this battery. Is this normal? How much run time should i get from two 2s 5000 wired together.

What is the rest of the setup, motor, etc?

Most likely need better batteries.

The setup is 8xl mm esc 20 or 18 / 46 gearing

Ok, you are running a 3s 4000 lipo on an 8xl with a MM esc.

First off I would step up to 4s, and lower the gearing if you are happy with the speed. I am suprised that the 4000 battery is not getting hot with your setup. If you go to 4s, you will have to remove the red wire from the signal cable (disable the bec) and wire in a ubec, or use a rec battery pack to power the servos. The 8xl is a great motor to run on 4s lipo, and will perform very well in your buggy.

Do you have a pair of 2s 5000 batteries coming, or just one?

Just one is coming (i own one already) For the bec i have the ccbec. im just waiting on the battery to come in. I have heared that you can get at least 20 min under racing conditions with this setup