Did they do any testing to be sure that it's a lipoma? My experience too has been that they tend not to make overnight appearances but I'm not a vet.
I have an old dog with several assumed lipomas, as well as a couple probably not lipomas which haven't officially been diagnosed, so I'm vaguely familiar with your dilemma and these would be my considerations (my dog is a poor surgical candidate due to health issues, and none of her growths are rapidly growing or in areas likely to impede motion, so it's an easy choice for me to leave them alone).
It's a rather difficult judgement call made even more so by your upcoming move. Because of the limited surface area of the lower legs, it can be difficult to remove larger growths on them due to insufficient skin to close the surgical site. It is usually recommended to have growths in such areas removed sooner, rather than later, due to that reason. At the same time, your dog is older, and if it is a lipoma, they more typically cause issues when they reach large sizes or are in such areas as to affect mobility. However, it's already quite large for that area, and waiting could allow it to grow beyond a size which can easily be removed, which may mean more extensive surgery by a specialist if it needs to be removed in the future. At the same time, if it is already of such size to be borderline difficult to remove, there may be higher incidence of post op complications, which could be problematic for your move.
It may be worth having your vet re-evaluate it at its current size, to see if they still think either approach (surgery now vs waiting) is equally acceptable. If so, that still leaves the decision completely in your hands, but they may have an inclination one way or another that may help you decide. Good luck with both the decision and the move