150ml is 3 times the amount you should to be aiming to use as a beginner.
You need to turn your gun setting down. If you are worried about missing bits and want to do 2 coats then you need your gun down really low so your using aprox 25ml per coat and therefore using 50ml for the whole tan.
Do the couch roll test to set your gun.
Spray 1 swipe of solution on to a sheet of couch roll from the same distance you spray your clients, if the solution wets the back of the couch roll you need to turn the gun down, repeat on clean couch roll until there is colour on the front of the couch roll but the back of the couch roll is dry.
3.18 to 4.30 of the video below Steve from Nouvatan does a couch roll tests & this is how you should set your gun, to use the least solution but still get a good tan and allow you to earn a profit.
When you get colour on the front but it is still dry on the back your gun is set correctly, with 1 coat slowly spraying a client (with the front of your gun about 6 inches away from them) you should use 50ml.
When you get more used to your routine and you speed up your movements you will start to use less solution and you should be aiming to use about 40ml when more confident.