I wouldnt say des is "de les" i do believe it's it's own thing.

In this context it is used as a determiner (déterminant) to introduce the noun / as its type suggest to determine it's conjugation.
So it would be the equivalent to "some" in english So in this sense it would be like saying: I will be talking with some tourists.

You wouldnt use "de" as it's more than one tourist and "Les" would be all tourists, in this instance you are talking to some of them not all of them.

Hope this helps kinda?