IMESSAGING LOCKING UP iphone 6 ios 9

iPhone 6 - 128gb (30GB available) / ios 9.0.2

iMessages lock up intermittently - either no response or can't send, close iMessaging and reopen usually does not help

Soft reset of phone usually works

Currently have 10.8GB of messages

Other large users of memory:

> photos 26GB

> audible 18GB

> music 17GB

Any thoughts?