To check the fluid, use the manual relief valve to release the trim/tilt mechanism
Open it three or four turns counterclockwise
I dont know where it is on a 150
On a 225, there is opening is on the starboard side clamp bracket
You can raise the motor manually to full tilt position then set the tilt/lock lever
On a 225 there are 2 round can shaped items behind the hydraulic rams
One with the wire is the electric trim/trim motor
The other one on the port side is the fluid reservoir and has fill nut (cap) in front
Open to check fluid
good luck