You’ve been doing that for 15 years. Cut me a little slack on trying to do it for five minutes.
Well, I understand the meaning of the second phrase, something like 'easier, I'm learning it for only five minutes', but I don't understand the construction of it. Is 'cut somebody a slack' an idiom?

Question

Answer

'To cut someone a little slack' means to go easy on them, to be less demanding or critical or to make allowances for them. The idiom originates from tailoring something to make movement easier.

Answer

When elastic is slack, it is not stretched, it has no tension.
The meaning is extended to ask someone to stop asking expectations, or stop creating tension.
I think you can figure out the rest from here.

Answer

Yes,it is an idiom.
'cut someone a slack' means 'give someone a break'

Don’t miss out on the opportunity to learn a language from the comfort of your own home. Browse our selection of experienced language tutors and enroll in your first lesson now!