Bottom line, Trek is replete with on-screen examples of super-sized objects that can move FTL. Heck, right out of the gate, the first produced series episode featured an alien vessel that was touted as "more than a mile in diameter." The Doomsday Machine was "miles long with a maw that could swallow a dozen starships." And of course,
there's Vejur.
So moving Spacedock is feasible based on what we been shown is possible so it comes down to
resources and
will. The Fed obviously has the resources and as for the will, well have you met Geordi LaForge?