It's a stretch, but I can reach it on mine. I do have long fingers though. But I rarely play above the 15th anyway. And if I need notes that high I prefer playing a 6 anyway.
I guess what I'm trying to say is that if you only go that high occasionally a Thunderbird should be fine, but if you regularly play that high you probably would be better off with another bass.
You should try one for yourself because that is the only way to know for sure if it is ok for you.
Clubs: Thunderbird #8,Gibson #39,Lakland Owners Group #23,U.S. Peavey #5,Short-Scale Six-String #3,Kala Ubass #3,Brice #6,G&L #57,Carvin #203, Bass Tattoo #41