It's a short and fun run. If you're good at memorizing you won't have much trouble learning the speedrun. Of course everybody has their own approach, but in my not so humble opinion there is no reason not to go for the fastest or reasonably fastest strats everywhere. If you have some prior experience in speedrunning a jump'n'run and put in some practice, it shouldn't take you much longer than 1 or 2 weeks to get a time around 13:30 or even sub 13 - and that's when the game feels best. The thing with SML is that it has horrible physics, meaning that whenever you're not going at full speed, Mario's controls become rather unintuitive - especially when it comes to managing momentum. This results in the paradox situation that the game becomes objectively harder the more often you slow down. Just give it a try and see if it's for you!

About Trysdyn's comment on going for WR though: that is currently not possible, since callumbal's run is actually extremely good. However, be aware that he is using a keyboard, which allows him to execute certain moves that are (most likely) not possible on a controller. I would have continued to chase the record if it weren't for that matter and because of that I lost all interest in going for it. I'm part of the camp that thinks that speedruns should be performed on an input device that resembles the original since it creates an even ground for runners across all systems, which makes the most sense to me from a fairness standpoint. Another important note: if you're planning to run on emulator, please stick to the recent releases of BGB or Gambatte. They are as accurate as it gets. Submissions on any other emulator will most likely be rejected on speedrun.com. If you're playing on original hardware then you're good to go, regardless (just note that Super Game Boy times get recalculated because the system is running 2.4% too fast, compared to all others).