Hey guys Alex is here to explain! The joke here has multiple layers! The first joke here is that the person said that it would take them “30 minutes” to cross that bridge because the original person said it takes “30 minutes to cross it.” So if it takes 30 minutes to cross, then you would of course cross it in 30 minutes. The second layer of the joke is that there is a different meme that shows that you can walk to a place in 10 minutes, but on the same image there is a person with rainbow in the background of them which makes it seem like they might be gay because of that, and for that person it only takes them 5 minutes to cross the same amount of distance. So, because of the fact that that meme shows gay people can walk twice the speed as the average person, they would then be able to cross that bridge in 15 minutes instead of 30!
And hey if you’ve read this far, you might as well follow! I explain memes like this all the time :) @alexplains_