Reduce simulation time in HFSS

I use HFSS to simulate a bandpass filter with WIDE gaps between its coupled lines. These wide gaps made the simulation time very long and hard to converge. In fact, very small meshes are required to correctly solve the problem.

Is it any trick to manage this problem?

I heard about spare lines in gaps (these spare lines should be assigned vacuum or air as material) in order to concentrate meshes in appropriate location. does it work?

Not particularly. A wide gap between coupled lines will need a relatively large mesh in order to be accurate. You could try setting up a seed mesh (I think that's what you're referring to by "spare lines"), but I wouldn't expect a huge improvement.