Like Dan said, you want to go a lot finer. I do about 45-60 seconds with the flair, usually going to 6 bar and then ramping down. I’m at around 10-12 on the Niche, which is substantially finer than I use with the dual boiler (it would choke). 15 seconds is definitely a turbo shot. Nothing wrong with that, but it’s not the sort of espresso I typically make.
My recommendation: go finer until you hit the point where you aren’t getting any water flow, then go a bit coarser until you can immediately peg the pressure you are looking for with control. There will be substantial resistance; patience is key, as with all things espresso.
I’ve pulled some long, think two minutes, ristrettos with the Flair 58 that were absolutely delicious. They were a workout.