Open Terminal and add the below code. Change the 15 to whatever amount of minutes you would like to set the default duration of a new event.
7 Ways To Be More Productive on a Mac Without Spending a Dime • Gear Patrol — Read on gearpatrol.com/2019/07/23/productivity-tips-mac-os/
How to reset the SMC in a MacBook (and why you might want to) — Read on thenextweb.com/basics/2019/07/23/how-and-why-to-reset-the-smc-in-a-mac/