Andrea,
Yes, 15 category 2-SDL is the maximum possible that you can claim and the PDUs from PM Lectures are category 4 (other providers).
Remember that the category of the PDUs are really not too important except in regards to the maxium allowed, like 15 is the max in cat 2-SDL. Otherwise, a PDU in category 3 is just as "valuable" as 1 PDU in category 4.
You may also want to listen to "PMI's PDU Secrets", which is the podcast episodes that goes into detail about this:
www.thepmpodcast.com/pdu