Nope. The worst selling mainline Final Fantasy since PS1 (XIII), still did 1.8m
Splatoon will have massive legs but Final Fantasy XV will outsell its lifetime to date in week 1 (800k-1.2m most likely), A 500k gap in favour of FInal Fantasy XV is the most likely outcome, as Splatoon current trajectory has it ending close to Mario Kart after 12months on sale ( between 1.1m-1.3m). It'll likely end its life 1.5m especially since next appears to be the Wii U's last. If it arrived at the beginning of a generation I think it'd have a better chance of beating Final Fantasy but still probably no.