There should be a fair number of direct buses from the main campus through to Grande Parade. The Number 25 will be the main one and I think still runs up to every 10 minutes during the day.
It could probably take 20-25 minutes to get between the two places, depending on time of day and how busy the bus is. I wasn't at Brighton or Sussex Uni, but I used to do a similar journey quite often, from not quite as far as Falmer to a bit beyond Grande parade and that didn't see too long at all.
So I guess it would depend on how much you want to stay in halls and what the alternatives are. For me, I'd want to stay in halls, but not everyone would think it a big deal.