How to say"别说那么快，让我想一想"in English?

我的是美语的说法，比较简单的：
Slow down，please. Let me think it for seconds.

Don't be too fast, let me see.
or
Slow down a little , let me think.

I'm sorry I can't follow you, more slower please.

Don't speak so fast, and please give me some time to think it over!