Unfortunately silicon hose is not fuel resistant. There are rubber hose reducers (collars) available, std sizing is in 1/4" reductions though i.e. 2" to 1.75"
You should be able to take a short piece of 1.5" ID hose and slip on the upper feed tube to act as a collar, this will increase the OD of that tube close to 2" where you can use a 2" hose and clamp it all together. This being the upper tube which is fitting down into the 2" hose it shouldn't be a problem as its only subject to fuel splash. Your tanks shouldn't be topped off to the extent the fuel constantly covers the hose anyway.
If you want something more than that go to a muffler (exhaust) installer and ask them to use there exhaust slip joint maker/expander to expand the end of the 1.5" tube to 2".