So the benefit will be barely noticable. As another comment points out, LTO should only be used when you need a binary optimized to within an inch of its life, such as a release copy, or a copy for performance testing.
Specifically, if LTO is so important that you need to be using it during development, you likely have a very exceptional case, or you have some big architectural issues that are causing much larger performance regressions then they should be.
WebAssembly and lightweight MicroVMs are enabling FaaS with real time code generation but the build toolchain makes it less appealing, when you don't want it to take half a minute to build or to be slow.
And factual.
I spent a few months doing performance optimisation work. We wanted to see how much performance we could wring out of an algorithm & associated data structures. Each day I’d try and brainstorm new optimisations, implement them, and then A/B test the change to see how it actually affected performance. To get reliable tests, all benchmarks were run in release mode (with all optimisations - including LTO - turned on).