[prof-dr-ir]

Good question, and the answer is not easy.

It looks like the proposed accelerator smashes electrons and positrons together which are nice and clean elementary particles (as far as we know), so much of the collision energy is directly usable to create, say, Higgs bosons with a mass of 125GeV.

At the LHC they smash protons into each other which at this scale are a bit like a soupy mess of quarks and gluons. So its 13 TeV c.o.m. energy actually gets spread out over multiple elementary particles, which might not even hit each other straight on. Because of this the number of high-energy collisions between elementary particles is significantly lower.

This is just my lay-physicist perspective by the way; an accelerator specialist can probably provide more details.