I wonder if they can build new F15’s.
They have never stopped. The F-15K is still being built. A good question would be to look at a new production model incorporating the F-22 systems, engines and maneuverable thrust. It would likely come out superior to the SU-30 and Eurofighter. It still wouldn't be the F-22, but it could be much more affordable, and add more strike capability to boot.
Ever since 9/11, the USAF has really been in an ever increasing budget fix, with funding being siphoned away for the Army and Marines in Iraq and Afghanistan. The service has lost over 40,000 personnel in recent years, and I'm sure that inspections, maintenance, and upgrades are being short-changed. The recent story at Minot about a serious breach in nuclear weapons handling and security no doubt has its origins in the budget and manpower crisis facing the USAF today.
But to get back to the F-15s A-D, their air frames are just wore out after 30 years of high G flying, and the entire fleet needs to be retired and replaced with F-22s. Pretty soon, I imagine, we'll be hearing similar airframe structural failures in F-16s, which entered service about 1979. Consequently, I don't think that the USAF generals are crying wolf this time around.