DunGen will generate dungeons you can download at 70px per tile, which is the default or better than most major tabletops, such as Roll20, Astral and Fantasy Grounds. Images are perfectly aligned so there's no fiddling required to make it work with your tabletop's grid and at that resolution they are optimized to always be below 5mb in size, the usual maximum for free users in major platforms.
Simply upload to your favorite VTT and you're good to go.