I see it generates tokens that are valid for 15 minutes, how can I increase this number? and would it be possible to be role-based increase/descrease?

You can't change the value at the moment. We can do it manually if you want though. It's not possible to do it per role via Hasura Auth automatically.

You can however generate your own access token using the JWT Secret that is available as a system environment variable. You can copy and use it, or directly use it in a serverless function using process.env.NHOST_JWT_SECRET.

https://docs.nhost.io/platform/environment-variables#system-environment-variables

can I do it manually in self hosted instances?

Yes

https://github.com/nhost/hasura-auth/blob/main/docs/environment-variables.md#:~:text=AUTHACCESSTOKENEXPIRESIN