May I ask all of you to speak slowly and clearly?

좀 더 명확하고 천천히 말씀해주시겠어요?

• Could you speak more slowly and clearly?
• Could you speak a bit more slowly and clearly?
• Could you all speak a little more slowly and clearly?
• I'd like for all of you to speak a bit more slowly and clearly.
• I'd appreciate it if everybody would speak slowly and clearly.