The most important thing is repitition and consistency when it comes to learning a new alphabet and character system.
5 minutes a day can be more adequate than 15 or 30 minutes a day. Don't think that the more minutes you do in a day, the more you'll learn/remember— if you've already got stuff going on, school, study or a job, or maybe some personal stuff going on, then it is going to be more difficult for your brain to effectively consume information, let alone learn/remember a new alphabet. If you have a fairly busy life then you may remember more if you study the alphabet (Katakana and Kanji) for a shorter amount of time, so your brain doesn't get overhwlemed and let information leak out in order to make room for more essential things.
Learning Kanji can be less about memorisation and more about association. In order to improve your memory of Kanji, associate them with something familiar. Or you could try memorising the English meanings of the Kanji and then their Japanese pronunciation (I find this is an easier approach, associating them with something I'm familiar with in my own language and then learning the Japanese pronunciation), rather than worrying about both the meaning and the pronunciation at once, which can get overhwelming and, in-turn, discouraging.
I found Katakana more difficult to learn than Hiragana. I think that's a fairly common thing among those learning Japanese. But all that means is that I need to practice Katakana more than I do Hiragana. Something I've found helpful in keeping me motivated is switching the language for my Netflix profile into Japanese— a lot of the titles on Netflix are in Katakana, so I practice my reading of Katakana when I take breaks to watch things on Netflix (a lot of the subtitle options also use Katakana, so you actively need to try to read Katakana to get the subtitles the way you want, too).
That's just my take on it. But I've struggled with learning Katakana and Kanji, too.
Just remember to not constantly compare yourself to others. Be patient with yourself, especially when it comes to something like learning another language (most people are unaware of how learning a language impacts your neurology and encourages your brain to work differently and adapt to the new language/way of perceiving the world) we don't all think the same, so others will learn slower and some differently, using methods that may work for them but not for others. Usually, learning a language can be just as much of an art as a science.
And if you're wanting better advice then I would recommend watching some videos or reading some articles on the best ways to learn a language in general, you can find a lot of helpful tips from linguists, psychologists and neurologists on the subject that may be of note and encouragement to you.
