We could build a more or less arbitrarily large rocket in orbit by adding more and more fuel. More fuel means more delta-V means the probe is faster.
https://en.wikipedia.org/wiki/List_of_artificial_objects_lea...
Long story short: they plan these out for decades at a time, and take your best shot when the planets align, literally.
If you can build larger ships in orbit, relatively cheaply, you can go a lot more direct, a lot faster.
Tsiolkovsky's equation shows how much dV you get with a given wet : dry (empty) mass of a rocket stage. Very quickly it's becoming very inefficient.
Unless you are talking about some untested rocket that dumps empty fuel tanks in pairs. (Like in the dV book by Daniel Suarez).