It makes no sense to use dt in 'Every X seconds', it's already measuring in seconds!
The simple answer is to make fewer collision checks. Only collision check objects which really need it, and try to only check every few ticks if possible. Alternatively try to spread your objects out over a larger area and collision cells will reduce the collision checks for you.
BTW if that's 1600 a second, that's almost nothing to worry about at all. A single collision check is near-instant, and 30 a tick or so will have probably zero impact on performance (not counting poly checks).