My brother who worked for McDonnell Douglas (now Boeing) on the F-18E/F project, told me about this tail. The engineers at MD said that the because of the shape of the plane body, something they had not foreseen, the fuselage acted like a lifting body when the plane was above 200 knots speed...
The F-15 was design started in the late 60's and went into production in 73'... It is a old airplane. It just happened to be the best fighter for the last 30 years,,, The F-15/14/16/18, MIG-29/31/Su-27, Eurofighter 2000, Panavia Tornado (there are more) are all considered a fourth generation fighters. The new F-22 and F35 are considered fifth generation planes and it will be 10 to 20 years (guesstimate) before someone other than us (US), that will be able to build a fifth gen plane... most likely the Russians....
The UK are buying the F-35... and maybe the Australians....