To what extent does security slow things down in your business?

Ideally if you integrate it properly it will actually speed things up in your business. Security can be a business enabler if framed the right way

"Slowing things down" implies a bit that the security processes are not considered as being an enhancement to the delivery. Another way to phrase the question could be "How frequently are security issues discovered late in the delivery process slowing down the time-to-market", or "How well integrated are security measures in your organization ensuring an efficient delivery of your products".

One could interpret the question as "if we would not have to consider security, how much faster would we deliver". But that's almost the same as stating "if we would not have to consider the functionality of the product, how much faster would we deliver", or "if we would not need to test things out, how much faster would we deliver", and that has little sense.

There is always a tradeoff between security and convenience.  More of one generally means less of the other and vice versa.

Depends on the situation but not all the time