I've been lifting for 3 months I've had a 3 week break because of schoolwork and other stuffs. Looking to cut weight to get down to 10% body fat. I was at 18.5 in June not sure what I'm at now. 5'8" 155. Biceps 15in. Bench 135x15 Bicep curl 32.5x20. How am I doing so far and how quickly can muscle deteriorate if I don't go to the gym?
You look kinda skinny to be cutting weight. I wouldn't worry about the 3 weeks, though.
The fact that you listed your bench and bicep curl numbers indicates that you'd probably be better off on a different workout than what you're doing.
You'll probably look a lot better physically if you allowed yourself to get to about 170ish+ and bench 200lb+/squat 300+lb/deadlift 400lb+ before you choose to do a cut.
No-one cares how much you bench for 15 reps, no-one cares how much you bicep curl full stop. The fact you chose these two exercises speaks volumes about your approach to lifting.
It's hard to say how you're doing so far, because you haven't given us much in the way of useful numbers. Likewise it's hard to say how quickly muscle will catabolise without a lot more detail.
I think you need to find a long term goal (think years, not months) and then people will be able to help you find a training approach that will get you there.
Forget about bodyfat percentages. They're too difficult to measure, even for trained people, and they're too arbitrary with no real world value. Stick with tape measurements, pictures, the mirror, and your performance in the gym.
Not trying to tell you your goals, but losing weight/getting smaller is not the right call here. Building muscle is. At your age (15, for those who hadn't noticed), you need to build a foundation of strength and muscle that'll set the stage for big gains over the next few years. Trying to get awesome abs is very short-sighted.
You told us your arm size, bodyfat, and your bench and curl strength. That's all pretty pointless and out of context, but it's also the typical focus for younger kids.
Benching 135x15 when you weigh 155 is pretty good, but I have to guess that you over-focus on that lift, which can definitely set you up for strength and muscular imbalances in the near future.
What do you squat, deadlift, row, and pulldown (or chin-up)?
I don't know why this is even a concern of yours, because it should be the last thing on your mind. At your age, there's seriously no reason why you can't get to the gym consistently - I didn't say "a lot", I said "consistently". Lifting 3 times a week for 24 weeks will deliver better results than 6 times a week for 5 weeks.
Check out the plans and the simple nutrition stuff I talked about here. That should get you back on track:
Also: fyi, those aren't 15" biceps in the picture. Unless you mean they're 15" long, and even that's pushing it.
You're already looking strong and have great potential, you should keep progressing in the weight you're lifting for a while, even if you don't loose bodyfat during that time you'll still look much better with additional muscle! Then consider cutting a bit if you wish.