Pressure in king keg how long to build

[scoobydoo]

I'm fairly new to brewing and have only made a couple of kits.
I've recently brewed a Wilko thirsty red and had this fermenting for 16 days before transferring to a king keg and priming with sugar
I've got a pressure valve and after 15hrs the pressure has only raised to 2psi.
On a.previous stout I had 6psi within 12hrs.
Just wondering how long should it take for the pressure to build?

 

[Buffers brewery]

I usually leave mine for a couple of weeks to carbonate. Gets to maximum pressure after 4 or 5 days.

 

[Agentgonzo]

It'll vary from batch to batch. Different yeast etc. Your previous batch may have had more yeast or active yeast left in suspension.