How to choose the right method of authorization and authentication?

Question

OAuth

Hello. I'm making a REST service in Spring and want to add a Spring Security layer. Since I don’t have development experience, I found this article on habrahabr.ru/post/245415/ which tells how to add security well, but it doesn’t say when and which method to choose. My application works with frequent requests (the client sends some data every 2-3 seconds and requests others). Now the questions:
1. Do I understand correctly that in the Token Access method, with each request, you need to decrypt the token, check the decrypted login and password with those stored in the database, after which only provide access to the resource? Wouldn't that be a big load on the server with frequent requests?
2. Still, I would like to hear your opinion, which method is well suited for a service with frequent, small requests to protected resources? Possibly OAuth?
Thank you all in advance.