15 years since 9/11 - in another 15 years will there still be Islamic terrorists?

Saudi Arabia has been the ideological engine room for most Islamic terrorism, including 9/11 

Probably. Back in the 1970s most terrorist acts were committed by nationalist extremists (such as ETA, the IRA) or by communists (such as The Red Brigade, the Bader Meinhof gang). But Muslim terrorists replaced them in the 1980s and the numbers have increased massively since then.

Since 9/11, the number of terrorism deaths worldwide has increased ninefold, although the bulk of it is in just five countries - Iraq, Afghanistan, Pakistan and Syria (in the Middle East) and Nigeria (in Africa) - according to the 2015 Global Terrorism Index,

Wahhabism in Saudi Arabia, which that country has actively exported around the World with a tsunami of money from its oil revenue, has obviously been a major influence for the Sunni Muslim terrorist organisations. But as that revenue shrinks from an international switch away from fossil fuels to renewable energy, as well as more efficient internal combustion engines, that factor will diminish. 

However, terrorists fulfill their perverted and depraved psychological need for violence and an end to their lives that they don't like, and that will always exist.