Invulnerability and Unlimited Ammo
Go to the Main Menu and enter the options screen. After that, go to gameplay and select settings. Now look at the bottom of the screen, it will say: "Cheats= Invulnerability and Unlimited Ammo" with boxes to check if you want them on.

Fly any plane
I'm not sure whether these are cheats or just some programing errors, but I consider them cheats. This is one of the discoveries I found in Janes F-15:

When you are in the mission builder YOU can fly any plane in the list.

Make a new mission, edit a campiagn mission, etc. Choose the human plane (your plane) and choose a plane other than F-15 (eg. SU-27, Mig-29, etc.) when you fly the mission campaign or whatever, the cockpit will look like the F-15's, but press F8 (exterior view) and see the difference!!!

Note: My F-15 is version is 1.02F and I don't know whether it applies to newer versions.