There is a good news for Sprint Galaxy Note 5 users, you will start receiving Marshmallow update starting 24 March.
According to Sprint, They will be releasing a software update dubbed PC3 for Galaxy Note 5 and it will be bringing Android Marshmallow, Google and Samsung Security updates and Bug Fixes. Sprint have also stated that they will be providing updates in a phase the update will begin rolling out from 24 March and will go on till 8 April. So, if you didn’t receive update on 24 March don’t freak out it would be coming in next few days.
To check for updates you can go to Settings>About Phone>Software Updates>Check for Updates.