#1 - 10 or 15 minutes is NOT slow - it is extremely FAST. I mean incredibly fast. Not even medium. Slow would be like 60 mins.
At least it's much slower than this trend of (hyper) turbo tournaments with only 3 to 5 minutes. Online there is not much options of playing in slower tournaments than the 10 to 15 minutes at the smaller stakes.
#2 - The faster the tournament is, the more luck is the major factor, the slower the tournament the more skill becomes a huge factor.
That's why I like the slow tournaments, usually the slower the better. I have a very good and long attention span and I don't get inpatient like many others. These things give me a nice advantage over my opponents, especially deeper in the tournament. Just have to survive the beginning.
#3 - It is not just the clock that determines the speed of a tournament - starting stack size is a big factor.
True, but here again, if you play at the smallest of stakes, the options are very limited, and a stack bigger than 3000 (or exceptionally 5k) is nearly impossible to find for me. But don't hesitate to share if you know some
However, usually when a tournament is slower they give a bigger stack than with a hyper turbo, but there are quite some exceptions to this though.
Your approach on fast or slow tournaments is radically different from one another and you should do what you can to adapt to and become comfortable with each style. "Cracking the code" on a tournament's structure goes a long way to consistently sitting at the final table.
Playing a 3 min vs 15 min blinds tournament is indeed totally different. They are two different games with each their way of handling. That's why I think, as a beginner, one should focus on one kind of game, something like NLHE 9 max 15 min tournaments.