If you present yourself as
Senior Design Engineer
i.e. with an English job title, the Senior is of course fine.
If you want to use German terms you can say
Leitender Entwicklungsingenieur *)
but that would be pretty unusual. Today, in the larger industries, almost everything is called by English names, just glued together with some German grammar. The big boss in a company is today almost invariably a CEO, nobody calls himself a Generaldirektor any more (that's a term from about 100 years ago).
Still, if your job title is not that specific, you might prefer a genuine German title such as
Leitender Ingenieur :-)
Senior Engineer :-(
And of course, for jobs that have traditional, well-established German titles you use those. You would not present yourself as a
Baker, Carpenter, Machinist
but as a
Bäcker, Tischler, Dreher (or Industriemechaniker or whatever)
*) If that's what it is. I am not in design engineering. But dictionaries say design engineer is Entwicklungsingenieur. I personally would have guessed Produktdesigner, but I may be totally wrong with that idea.