2.25% of both hitting sets.

But there's only a 40% chance that 2 people are dealt pocket pairs.

And this is assuming that their PP is smaller than yours.

But one thing you do have to factor in is that big pocket pairs will generally see 4 or 5 cards rather than just the flop.

Whatever the result, if you pretended set over set possibilities never happened you would be making a very small mistake.