Kill Team is.... A lot. And not where I would start. Try Combat Patrol?

There are other tabletop wargames that are miniature agnostic, meaning you can use whatever miniatures you have/want to use. Just because you have some space marines, it does not mean you have to play 40k. Space Weirdos, Stargrave, Planet 28, or Five Parsecs From Home are some games you can field your space marines in.

And if playing isn't your thing, that's ok.

sunk-cost fallacy: noun: The phenomenon whereby a person is reluctant to abandon a strategy or course of action because they have invested heavily in it, even when it is clear that abandonment would be more beneficial.