Fifteen weeks, 5.75 lbs.
The average, says the vet, is a pound a month.
Murdercat at 14 weeks was about a pound lighter, and he turned out big. He was also, at that age, in his lanky phase, all knobby limbs and tail and ears.
Orion still looks like a young kitten, proportionally. He looks small until you get up next to him, or see him next to Tinycat. Look at those feet. Look at those legs. He's going to be big, I (and Nous, and the vet, and everyone else who's seen him) think.