You havent enough light to flower. In the space you have, you will need at least a 250w HPS, with a parabolic reflector (because the rectangular shape). In you can cool the space adecuately, a 400w HPS make sense.

T5 arnt the best to support low areas, because they run hotter than T8 and can burn your plants.

Other option avalaible is using floro tubes and scrog. You can use T8 30W (35 1/2") or T5 HO 39W or T5HE 21w (both of 33 1/2 "). You will need at least 8 tubes.

If you want to use the equipment you have, and you dont need too much yield, the best you can do is divide your cab in 2 areas, one to veg with mums, and one to flower. If you are going to use a 150w HPS, notice it havent much penetration, so use it doing scrog or put it hanged vertically bettwen 4 plants (no larger ones) in a space of 20x20".