My tire was slashed. Replaced the inner tube, but should I replace the tire as well? Talking about a hybrid bike.
As the title says my tire was slashed. It happened overnight and the cut is on the side, so I'm 99% sure it was slashed. I replaced the tube and have been riding without any further problems for a while now. However I still have a ~1.5cm cut in my outer tire. My question is whether I should be concerned and whether I should replace it?
You already know the answer to this question.
Slashes in the sidewall tend to open up as the pressure from inner tube is pushing the tire further apart. If you're lucky you might escape with a simple pinch flat. More serious problems include:

the inner tube pushing through the sidewall rubbing on the frame or fork causing the inner tube to burst like a balloon.
the inner tube removing the bead of the tire

Either of these I wouldn't want to happen at speed.