I did a brisket on the 4th at exactly your temps. The temps climbed to 150ish within the first hour and a half to two hours. Then they stalled for quite some time. It took about 9 hours and 190* or so but probed really tender when I pulled and wrapped it and into the cooler it went for a few hours. It'll hit the stall for a while and climb up really slowly. I check around 180* to see if it's probe tender then pull it. I don't solely go off temps. Probing tender determines when I pull. The temp is just a rough estimate for me.
A question for you. Are going to pull at 155 and wrap it and rest it or are you pulling it to wrap and throw it back on the grill until 180-190? 155 is way to early to pull the brisket off and let it rest.
36" DCS NG Grill - Vision Kamado PRO - 36" Blackstone Griddle LP-'10 Weber Performer-PBC