Asking to repeat more slowly.
If I want to ask someone in Japanese to repeat something more slowly I found a resource that said I should use "mou ichido yukkuri shiteimasu itadakemasu ka" but I also heard that "itadakemasu ka" is very polite.

Is it too formal for casual use? Should I maybe exchange it for something like "o kudasai"?

I don't want it to sound rude or abrupt, but also not like I'm talking to my boss or someone very high above me.

I am learning to speak, not write, so please use romaji in your reply.

Thank you!

Question

Asking to repeat more slowly.
If I want to ask someone in Japanese to repeat something more slowly I found a resource that said I should use "mou ichido yukkuri shiteimasu itadakemasu ka" but I also heard that "itadakemasu ka" is very polite.

Is it too formal for casual use? Should I maybe exchange it for something like "o kudasai"?

I don't want it to sound rude or abrupt, but also not like I'm talking to my boss or someone very high above me.

I am learning to speak, not write, so please use romaji in your reply.

Thank you!

Answer

Hi;)

Yes, if you say "mouichido yukkuci hanashite itadakemasuka" it sounds like you are talking with someone very important, so firstly  let's modify it with "kudasai". It can be

mouitido yukkuri hanashite kudasai

this sentence is correct, you can use it;)  but I also  think that it is not perfect because in Japanese when you want to ask some action to other people you should better give them options but if you use "kudasai" it's polite but an order.
So I offer you this sentence

mouichido yukkuri hanashite moraemasuka?

"moraemasuka" tastes like "could you...?" but we often use it and it sounds more soft, feminine, educated and without any aggression. You can use this form to any people;)

Answer

Hi! I'm not perfect in japanese but I usually use these phrase when speaking with my sensei:
Mou ichido yukkuri hanasite kudasai.

It seams to be not so rude:))