I would like to change the default terms in invoices to Net 15. At the moment the default is Net 30 and I can change this to Net 15 but I often forget to.

Hi konnichiwakidscl,

Welcome to the Community! You can set up a new Net15 term for your invoices in your Company settings and then, select the All List section. Here's how:

1. Click on the Settings Icon at the top right.
2. Click on All List.
3. Click on Terms.
4. Click on New button.
5. Enter a term name, select the Due by certain day of the month radio button, then enter 15 in the day of the month box.
6. Click on Save.

You can also check this article about payment terms in QuickBooks Online: 

• Fix inconsistencies in due date and invoice date in QuickBooks Online 
• How to Adjust Invoice Payment Terms in QuickBooks Online

Keep me posted if you have any other questions. I'm just around to help. Have a great day!