Could you tell me how important this is? / Do you mind telling me how significant this is?
Right now, we're in pending negotiations with them, so if it isn't that important, can it wait until after the negotiations are finished?
We're currently negotiating with them, so if it isn't that significant, is it OK to wait until after negotiations are done?
「どれぐらい」は英語で「how」になります。
「重要」は「important」または「significant」という形容詞です。
Could you tell me how important this is?
Do you mind telling me how significant this is?
それってどれぐらい重要か教えてくれませんか。
「交渉中」は「pending negotiations」または「in the middle of negotiations」です。
Right now, we're in pending negotiations with them, so if it isn't that important, can it wait until after the negotiations are finished?
今、彼らとは交渉中だから、そんなに重要な用件ではなければ交渉が終わってからでも良いですか。
We're currently negotiating with them, so if it isn't that significant, is it OK to wait until after negotiations are done?
今、彼らと交渉中だから、そんなに重要な用件ではなければ、交渉が終わってからでも良いですか。
Could you tell me how important it is?
How urgent or important is it?
特に今回のように、顧客対応の優先順位を判断するために、同僚に丁寧に確認したい場合は、**how important it is** や **how urgent it is** という表現を使うと自然で適切です。
アメリカ合衆国 
