I am terribly terribly confused. Of course, this may just be me?
- What is a "travel biography"? Is it a biography of someone who was famous for their travel (T. E. Lawrence, Freya Stark, Patrick Leigh Fermor, etc.)? Or are you talking about a memoir of your own travels?
- The word count is perhaps twice what it should be; if you look at other books in the travel or memoir subgenres, 100K is an unusually long book. For the biography subgenre, even for a biography of a super-famous person who lived a long life, 150K would be an unusually long book. I would be concerned that an agent who didn't flag that for you would be unfamiliar with the conventions and markets for the subgenres.
- Three weeks is certainly not long enough for most writers to complete a biography or a travel book. If this is a memoir, then yeah, it's best to wait to query until the book is completed.
I don't know what I would do in this situation except to say "Three weeks isn't going to be possible for me; I will contact you once the book is completed and see if you are still interested at that time" and then go on either querying from the proposal and sample chapters (if this is a biography or a travel book) or complete the book and then query (if this is a memoir).