I am assuming both the PFU and the cell count number are per ml? But if you have 1.5x10e8 cells and want an MOI of 0.01, then you want 1.5x10e6 PFU. You can adjust the math because I don't really know what volumes you are working with.

for MOI of 0.01 you need 1.5E6 pfu. Assuming your viral stock is 4 X 10 E10 PFU/ml, you need 3.75 microliter of your stock for infection.

You want to add enough virus to infect roughly 1% of your target cells. You have 1.5*10e8 cells, so you need to get 1.5*10e6 cells infected within the same time frame you performed your titration (pfu estimate) in. Depending on the unit (ml or ul) of the virus prep titer and the volume you usually add to the target cells during infection and the number of replicates you do, you can calculate what volume of virus prep you will need to dilute to achieve your goal. It is always a good idea to add an extra to your replicate number to account for pipeting errors.

Virus stock titers:

4X10^10 pfu/ml ->40 folder dilution ->1X10^9 pfu/ml

Set the volume as X,

X ml times 1X10^9pfu/ml divided by 1.5x10^8 cells=0.01 pfu/cell (MOI)

X=0.01 times 1.5 x10^8 divided by 1X10^9=1.5X10^-3ml =1.5ul

Based on your description, you will need 1.5 ul 40-folder diluted virus stock.