The use of the RDS mysql processor is 90% greater than always for less than 250 connections (conn 1236 max)

I use mysql RDS db.m3.xlarge (4 vcpus, 15G ram). The maximum number of connections is 1236, but more than 90% CPU is used for less than 250 connections. I do not know what I'm struggling to find the reason. Please help?

What should be the ideal value for innodb_thread_concurrency for the above configuration?