Hey,
A few things to work out whats going on.
1. First, replace the tiles with the default Unity box. Do you get performance issues then? I suspect you would, as the tk2dSprites are just plain meshes there. If not, that implies that something could be wrong with the dynamic batching, etc.
2. If you have Unity pro, just turn on the profiler and see what is taking up the most time. It should be obvious even when running on Mac. You obviously have a pro license on the mac anyway, so you could try that. Also, if you don't have iOS Pro, you can enable the profiler in one of the .mm files in xcode, can't remember which one offhand. That'll tell you whats taking the most time.
3. These aren't animated sprites are they? Animated sprites do take quite a bit of time to update, so having a lot of them all animatiing at the same time could be bad - there are ways around this.
4. I dont know about the colliders - test #1 and #2 will tell you if the colliders are the slow bits.
Let me know what you find and we'll take it from there.