Confirmed. Definitely takes too long.

Some numerical analysis with varying amounts of data suggests that it's O(n^2).

Right, I've slapped it about a bit, and two lines of code dropped the time for 115 items from 8643ms to 90ms.

However, 4179 items still takes 115095 ms. I'll take a look at that later.

In the meantime, at least you'll get an hourglass.