I know how much effort you've put into Plan A, but I think I would like us to go ahead with Plan B instead.
Because I don't think Plan A is working.
ご質問ありがとうございます。
"I know how much effort you've put into Plan A,"＝「あなたがプランAにどれだけ努力を費やしたか私は知っている」
"but I think I would like us to go ahead with Plan B instead."＝「でも、代わりにプランBで進めて欲しいと思います。」
"Because I don't think Plan A is working."＝「なぜかというと、プランAはうまく進んでいないと思うので。」
ご参考に。
アメリカ合衆国 
