On my system (Linux 64 Bit) I figured out that python 3 needs a little more memory than python 2 and it is a little bit slower. Here are some examples:

sworddragon@ubuntu:~$ execution-time 'python2 -c print\("0"\)'
0.21738
sworddragon@ubuntu:~$ execution-time 'python2 -OO -c print\("0"\)'
0.22559
sworddragon@ubuntu:~$ execution-time 'python3 -c print\("0"\)'
0.37962
sworddragon@ubuntu:~$ execution-time 'python3 -OO -c print\("0"\)'
0.37825

Checking the memory usage after python 2 and python 3 are started in a terminal shows the following:

python2: RES 4780 / SHR: 2212
python3: RES 6168 / SHR: 2660

What is the problem? 
Python 3 uses more memory because many things that were earlier ASCII strings in Python 2 are Unicode strings. Same reason for performance AFAIK.

The "performance" you're measuring here is mostly startup, i.e. loading all necessary modules.  On Python 3, there is more to load, e.g. the filesystem encoding, therefore startup takes a little longer.

There are efforts to improve startup time, see e.g. #16101.

The memory consumption is expected, again due to more modules loaded.  You cannot make any statement about the memory usage of a real-world application by just measuring the overhead of the interpreter.

The memory usage due to strings should be very similar to Python 2 starting with Python 3.3, due to PEP 393.