Darth Vader Force Crush Ending Prematurely

Vox

So i've been wanting to try a team makeup that boosts culling blade. Currently im running with Sidious Lead, Vader, Kylo(Just cause hes nicely balanced and riposte + AOE and his single attack has a dot chance), Luminara, and Daka.

What ive been noticing so far though is that before Vaders turn comes up again dots are falling off before he can even use culling blade. Is there any other ways i can make him not as slow? I've seen combos with vader work really well in this regard and i dont know what else i can do.

Thanks!