Open PNL in getCashBalanceSnapshot

As part of trading strategy I want to constantly monitor Open PNL.
getCashBalanceSnapshot seems to be the only API that gives open PNL, but it is a post API and discouraged to use frequently
Two questions
1- Is there any other API that I can use to get Open PNL?
2- if there is no other API, how frequently can I call getCashBalanceSnapshot?