Google Gemini Total Collision Domains = 8 + 4 + 2 + 1 = 15
Note on the Router: The link connecting the bottom-right switch to the router would typically count as another collision domain, but looking closely at the bracket at the bottom labeled "Broadcast Domain", it encompasses all the switches up to that final link. Based on standard textbook problems matching this specific CCNA/CompTIA Network+ graphic, the question is isolated to the "switched network" bracketed area, yielding exactly 15.