If you post the code (or better yet the file itself), maybe someone could help you optimize it.
Without seeing the whole form it is hard to tell. There are ways, like using functions and careful placement of JS actions, that can improve the performance of a form.
I am unable to supply the form, but below are 2 examples of the code used;
var a = this.getField("Weekly Amount");
var b = this.getField("Package Discount");
event.value = a.value - (a.value * (b.value/100));
var a = this.getField("Weekly AmountSubtotal abc");
var b = this.getField("Multimedia Discount");
var total = (a.value * (b.value/100));
var fixedTotal = total.toFixed(2);
event.value = fixedTotal;
Any help would be appreciated.
And where did you add the code?