using vba code with if formula

Hi all,

Is anyone assist me using vba code with below formulars?
p15=IF(H15="","",TRUNC(L15*N15,0))
p15=IF(H15="","",TRUNC(IF(R15>AC15,AC15,0),0))
p15=IF(H15="","",TRUNC(R15*$H$8,0))
p15=IF(H15="","",TRUNC(ROUND(X15,-2),0))

because of such formulars are p15:p5000, the excel speed is so slow, that is why I want to use vba code instead of the above formulars.

Thanks in advance

Originally Posted by Palmetto

Cross posted at Ozgrid

Sorry to make cross post, I just try to get answer earlier.
I will keep the rules