Hey people, lets put a bit of facts to our debate shall we

1. F-15 design is NOT as old as some of us would put it. The F-15
and F-16 design pretty much came around about the same time, almost
liken to the F22/F35. USAF back then, had the same requirement of a
hi-lo mix and thus the F15 representing the High (air-superiority),
and the F16, the lo, light weight fighter with minimal detection
and weapon carrying capability. Of course, these 2 designs have
evolved over the 2 to 3 decade of their services, especially for
the Viper. The Eagles, no longer serves as just an air superority
fighter (btw, the Russian effectively counter the Eagles/Vipers
with Fulcrum/Su-27 hi-lo mix), but one with long range strike
capability (somewhat to complement if not totally replace the F111
of the Vietnam war era).
2. F-16 Block 60 is NOT anything like the Block 52s RSAF has. The
difference (in broader sense) are:
i. different engines (similar powerplant, different ratings,
32,000lb
PW F100-232 compared to the 29,000 lbs PW F100-229.
ii. avionics will be vastly different. Different radar (Block 60
will have a Northrop Grummans APG-80 AESA), higher-speed mission
computer, a new display processor, 3 large colour LCD displays,
advanced data transfer unit with a fibre-optic data transfer
network Precision targeting is achieved by the Northrop Grumman
integrated navigation FLIR and targeting FLIR system using mid-wave
infrared arrays and JHMCS by default.
iii. Block 60 has an integrated FLIR. RSAF still relies on LANTIRN
pods.
iv. Block 60/62 F-16 would also utilise some technology developed
for the F-22, eg. the fusion technology, data sharing, etc. Block
60 frames will be able to share data among themselves and assign
targets or track zone, etc. Current Vipers cannot do that.
v. CFT, although this can be retrofitted to current Vipers.
vi. Different electronic warfare suite. It will have the Airborne
Self-Protection Jammer (ASPJ).
vii. the list go on...
picture of an F-16 BLock 60 model from LHM:

Given all these differences, Block 60 Vipers can be almost treated
as a totally new aircraft. However, they do share similar parts
(engine parts, landing gears, and bits and pieces here and there -
they all add up) which helps in terms of logistics.
3. RSAF is NOT the last users of the hardy Skyhawks. Current
operators include:
1. Argentinian AF
2. Brazilian Navy (on their carrier)
3. US Navy (Aggressor)
4. Israeli AF (Trainer and Aggressor)
5. Indoneisan AF
6. RSAF (of course)
4. The last time RSAF operated an endangered species fighter was
the Hawker Hunter.
5. F-15T is also very capable. It is NOT a gen 4 nor a 3rd gen
fighter. It falls somewhere in between, perhaps a 3.5 gen aircraft.
Bigger issue I have with F15 is their RCS - too big. Too easy to
spot. Of course with the AESA radar, they sure can fight their way
out in BVR engagements. However, if they meet a small agile
fighters or the Sukhois, I hope the pilots get the first glance and
a Python 4/5 soon follows. Otherwise, God helps the pilots).