Actually, the one who will be more under pressure for the match is the host, Dortmund, because Bayer Leverkusen will still try their best to win in the away match. Moreover, Leverkusen is currently only four points behind the top of the Bundesliga standings so Leverkusen will do their best to get full points at Dortmund's home. In addition, Dortmund this season has not been very consistent in winning matches so Leverkusen will take advantage of this when they come to Dortmund's home.
I agree with you that Dortmund are the one under more pressure to win the tie but Bayer Leverkusen themselves have their own pressure to deal with as they will want to start the second phase of the title defense mounting pressure on the leaders Bayern Munich, so for me this kind of games sometimes do not go with the form of each club but the intensity is usually up regardless of anything just because of the rivalry between the two clubs. Take for instance last season even with the super form that Bayer Leverkusen were on they could only managed to actually take draws from Dortmund in the both games. This season Dortmund remains formidable at home and as such wouldn’t be easy to get pass them