Welcome to the Ranch.
First off, do you understand what your manager is trying to achieve? Look at the code, does it actually or seem to do what he wants? I assume you do.
Forget about performance. Forget about if the code is documented.
Writing correct functional code is key. If you understand the code as is and its purpose then you are in a position to criticize or nitpick it.
Now do you know a better approach to solve the same problem? This includes algorithm, syntax use (eg while vs for loop), API usage (don't reinvent the wheel) etc.
The last thing
you should concern is performance. Of course unless your code is for those low latency stuff.
At the end of the day, KISS and don't complicate things more.