I don't have experience with your particular cell line, but generally, for suspension cells I am using in between 20 ml and 40 ml of media. I think some companies recommend 30 ml. 15 ml is too low in my opinion. The other thing is that you should check in the cell line datasheet or in some publication which density the cells should have.

Hi, I work with the human version of MEL cells. I always try to keep the concentration between 0.2x10^5 and 2x10^6 cells/mL. If the cells still seem to dense, then maintain at 1x10^6 cells/mL. But yes, the cells grow very rapidly, and needs to be given fresh medium every 2-3 days. 

'Woking volume of medium in T -75 cm2 flask is 15-20ml. If you find more density of the cells you can split into other flask rather adding  medium to the same falsk. more addition of the medium can prevent the aeration of the cells growing in the incubator under 5%of CO2.

Thanks Daniela, Nur-Taz and Manchala, that was really helpful!

with suspension cells just use 20 ml instead of 15 ml.

Hi, usually when I start to culture suspension cells I start with 20ml then based on the number of cells you can decide to add medium to the same flask or centrifuge and put them with new fresh medium in a new flask

I don't have experience with MEL cells but for A549 cells(adherent cells) I am using in between 10 ml to15 ml of media in T75 flask.