Email Alert based on Previous Document Create Date

Hi Everyone,

Is there any way that I can setup an email alert based on the previous document create date.
For e.g., User X has created a Material Request on 1-Jan-2016

Case 1: If the request is not converted into Supplier Quotation within 15 days, then user X will receive an email for the same.

Now User Y has created a Supplier Quotation based on Material Request on 12-Jan-2016

Case 2: If the Supplier Quotation is not been converted into Purchase Order within 15 days then user Y will receive an email for the same.

I appreciate, if anyone can help me in this regard.

Ruchin Sharma