Sure, just different ones. Compiling Guix and its package modules (aka 'guix pull') takes minutes on powerful hardware, and is nigh impossible on low-end systems. Computing derivations that import a lot of Guile/Guix modules can take some time for the same reason. These computations are cached of course, but still change frequently enough that you'll notice if you have to build them locally (i.e. custom packages not in Guix proper).
OTOH, Guix operates on in-memory representations of profiles, packages and derivations, and delays using the store until an actual build needs to be performed; whereas I believe Nix keeps making RPC's to the store during evaluation (please correct me if this is wrong).
I don't think adding Guix support to Tvix is as easy as plugging in a Guile evaluator, as the Nix tooling would not be able to understand the higher-level abstractions in Guix. You really need Guix and all its supporting modules to evaluate Guix packages.
Guix used to use the same derivation format as Nix, but they've since diverged