Hi there, nkadri.
I can help you change the VAT percentage from 5% to 15%. This can be done within the Tax page in your book. To guide you further, please follow the steps below:
In addition, we can add another percentage, which is 15% in the Invoice set up without changing the previous percentage. Here are the steps on how to do it:
Every time you want to add another VAT percentage, you can follow the same steps above.
Tap me on my shoulder if you have additional questions with this. I'll be around to assist you further. I hope you're doing good. Take care!