what atoll in the South China Sea does Singapore claim that it needs F15s?
It is all about China as the regional threat to everyone else over there
If Singapore did not have a spunky, totally kick-ass-take-names military with the highest standards of training, doctrine, and equipment, it would have already been swallowed up by Malaysia, which resents it for any number of reasons, not the least of which being its much higher standard of living, cleanliness, modernity — and the fact that it is an ethnic Chinese majority city surrounded by Malays.
With Muslim Malaysia (of which it was part until the 1960’s when they were kicked out for being “too Chinese”) and Indonesia to the south (the largest Muslim country on Earth) Singapore has every reason to be armed to the teeth. Especially since through hard work, clean government, and location on the globe’s most important and narrowest trade corridor they have during fifty years of independence become the jewel of Asia. The China threat may also be a factor but a distant third after their immediate neighbors.