I carb mine at 25psi and then drop the pressure for serving. If the CO2 tank stays on the keg with the gas on the whole time, it takes about 3-4 days to get a decent carb. Usually, I am trying to carb 5-6 kegs at a time and I dont have a manifold, so I charge each keg once per day. That takes about a week for all of the kegs to absorb the CO2
17psi in 2 weeks should work if you keep the gas on - Did you fill the keg completely to the top? That might make a difference. The rate of diffusion is a function of surface area as well as pressure, so you dont want to fill to where the keg narrows at the very top.