Slow work of rotary axis

I have 4-s axis on my linuxncnc machine. When it starts to work, all movement's become very slow and configuring speed with G1 Fxxx doesn't help's me. I've looked topics with such my problem and found that problem is that speed configuration changes from mm/min to deg/min. But I realy didn't anderstend, why axis not become faster when I change feedrate.
What regulates speed when works rotary axis? And how to control it?

You have give me very cool solvement, Endypugh.
I will try to use it on my very slow PC.

I tried to use filter.py but get error when load file.foam

Errors is "Permission denied"

get error 127 "file not found".
I tried 777, 755 and 666.
I don't understand why I get that filter.py file not found. It's present and pass is written to configs folder.
File has complite permissions now -rwxrwxrwx

I get exactly this error, when the path to the filter is not correct, example '/home/NcFiles/Filter/filter.py'

I checked my problem more presicely.
If permissions has number 7 (mean x-execute), then I get error 127 "file not found".
If I set permissions with number 6, then I get error 126 "permisions denied".

Possibly, problem is in something else.
in the directory usr/bin/.. I don't have file python, but files python2.6 and python2.8

Or could be problem that linuxcnc doesn't have permissions?
I had problem with reading python files by linuxcnc in the past. I didn't solved that problem.