Pricing rule linked to a field - looking for fast and simple method to create pricing rules

Hey,
I’m looking for some simple method to add pricing rules for my customers based on my purchase discount. I’ve already created few more fields and when importing items I’ve added my discount to every item. I would like to create rules based on that discount with simple logic.

Example:
In the field
Price Discount Scheme
Discount> Discount Percentage: [my_own_variable_from_item_docfield_representing_my discount]-15

Probably wood need some function like that: if([my_own_variable_from_item_docfield_representing_my discount]-15<0;0;[my_own_variable_from_item_docfield_representing_my discount]-15)

Maybe there is other faster way to create pricing lists for huge amount of items?