When I've developed games on other platforms, I've used Quadtrees. A guide is at
https://gamedevelopment.tutsplus.com...e--gamedev-374
Essentially you split the screen into multiple sections. If your character is in a different section than an enemy, skip the collision checking.
I've never implemented that in an Amiga game (yet?) but I imagine it would speed things up because you're saving cycles by not constantly checking collisions.