A minute amount of enzyme is required for any enzyme assay like 0.0001 to 0.01 mg/mL.

I have understood that your objective is the lipase activity evaluation. This is a balance between the reaction time in the applied conditions and the enzyme amount. The reaction evolution as a time function must be linear. You could apply a time sufficient to measure the reaction product or the substrate disappearance. Generally, the enzyme amount is very low.