Can I switch "talking" to "telling" here?

Rebecca

Actually, "we're/I'm talking" is a casual expression that is used to emphasize something. In this case, "we're talking ten times your normal crowd" is stated here to emphasize that this number is so much larger, so it's very much quite surprising/unusual. It doesn't really have a meaning on its own, its just used as an expression of emphasis. Ex: Joe got me the biggest bouquet of roses for Valentine's Day. We're talking hundreds of roses! Ex: I saw so many nice cars on the road right now. I'm talking Lamborghinis and Maseratis!