It's insane, he isn't even a "hot" character right now. He got some solid reviews on two "okay" selling books: the recent mini and the main series.
I can't speak for Suicide Kings, pretty sure it was close to selling out it's runs, but I know the ongoing Deadpool book sells out every month like clock work which is why he's considered hot by the editors, the runs are around 50,000, obviously he's no Blackest Night or Reborn, but that's pretty respectable for an ongoing that doesn't star the Bat.
As of today we have three Deadpool ongoings, that is a bit much, but if they're all good I won't complain since I'm a huge DP fan, granted Merc with a Mouth isn't as good as the regular book but Gishler is slowly finding his groove with DP and each issue has gotten a little better.