Frame with a tapered headtube - fork compatibility
The 1-1/8"-1.5" measurement actually refers to the diameter of the fork steerer tube that the bearings will accept, not the headtube of the frame. Your frame therefore expects a fork with a 1-1/8"-1.5" tapered headtube. You can use a straight 1-1/8" steerer fork with an adapter for the lower bearing.

Other geometry considerations are the axle-to-crown length and the rake. It seems that some road forks don't have a axle-to-crown length specified but are generally the correct length for a ISO 622mm wheel. Small differences in length will not make a difference to steering geometry. 

If you are looking for an MTB suspension fork, you need to consider wheel size and travel. I think there are a couple of dropout spacings used in the MTB world as well.