XF 1.5 configuration import

Normally, the default should be enough.
Depends on import size, what you import, your speed to internet and server / vps.

my values
max_execution_time 300
max_input_time 60
max_input_vars 3000
memory_limit 400

If they are too small for you, you can add X 10 to the top 3, and memory_limit rise to 1000.