I recently contacted Sony customer support about the Marshmallow release for the Xperia Z3 since it is posted all over the manufacturers website that the phone received the update. Obviously they are referring to the international version of the phone since the USA T-Mobile spec phone didn't receive it. I asked Sony if they had any information on the release for the US spec phone:
Dear Valued Customer,
Thank you for contacting Sony Xperia™ Online Support.
In regards to your inquiry, we understand that you would like to have information in regards ot the release of Android™ Marshmallow on the T-Mobile variant of your Xperia™ Z3 (D6616) and I'll be glad to assist you. However, I am sorry to inform you that we don't have vast information on the software of this particular device as it contains a modified version for T-Mobile.
In this case, the best we can recommend is to contact T-Mobile directly for the possibility of more information. We apologize for any inconveniences this may cause you though.
As part of Sony Mobile's commitment to excellent customer service, we offer a wide variety of mobile products to suit your lifestyle. If you require more information, or have any other questions, please visit www.sonymobile.com or call us at 1-866-766-9374.
Sony Xperia US Customer Services"
Based on that information it sounds like T-Mobile needs to get the ball rolling and give us some answers on this release. If it is already out there for the international version, how much more effort could it possibly take to make it work on the T-Mobile edition. Please let us know if there is any discussion on supporting this phone past Lollipop.