Is MacBook Air 2015 still worth buying?

Your biggest problem will be finding compatible software and security. You could use it as a Unix Device, or a NAS. but I would be careful of connecting it to the internet. If all you need to do is to record sound, consider a digital sound recorder.

You could use it as a standalone, and not connect it to the internet if it has the old logic x pro on it. I don't think you could get an old version for it now. If it comes with the Logic X pro, you can use it, but do not connect it to the internet. You should save on a memory card and then get a memory card reader if you want to upload it with another device.

Take a look at the difference in price between that and a Macbook Air 2018 which is compatible with Ventura...,.but probably only for the next year. The 2019 would be compatible for two years.

But the 2015 might also make a great doorstop! ;)

If you have to do some simple task, you can go for it. Simple tasks like watching your educational tutorials, and doing live streaming with friends and family members, you can do office work on it, and you can also do some accounting-related work if you're an accounting professional. But I will not recommend it for heavy tasks like video editing, designing and other things like that.

Thanks

No. It's just too old.

Minimum requirement for Logic X Pro is 12.3. What if it's upgraded? You would be better off asking in the Logic Pro forum: Logic Pro - Apple Community

My wife still finds our 08 13" MacBook useful. She has no need for the latest and greatest hardware or software. It all depends on YOUR needs.