Am I owed a debrief if the award was under FAR 8 or 13, or only under FAR 15?

You are not owed a formal debriefing under FAR Part 8 or FAR Part 13, as the requirement for a postaward debriefing is found in FAR 15.506. FAR Part 8 covers required sources of supplies and services, including GSA Multiple Award Schedule contracts. FAR Part 13 covers simplified acquisition procedures. Neither of these parts mandates a formal debriefing process like FAR Part 15, which applies to contracting by negotiation. The contracting officer for your GSA order gave you a courtesy call, which is common. For the simplified acquisition, the contracting officer was correct that a formal debrief is not required. If you want to protest, a GAO protest must be filed not later than 10 days after the basis of protest is known or should have been known, whichever is earlier (4 CFR 21.2(a)(2)). Since no debriefing was offered or required, the protest clock starts from when you received notification of the award.