The user interface has undergone changes and this starts when AutoCAD is launched.
For the use of this version 2015 one gets used to this interface which displays better visibility in different areas:

The Start AutoCAD displays a home screen
AutoCAD 2015 does not start with an empty drawing, but displays this home screen:
1. left more to access videos on AutoCAD: Overview of new features,
2. click Icon Start a drawing and choose from the drop-down list a template,
Or open and select a drawing
3. Open a drawing, choose from recent drawings.
4. Right to connect to Autodesk 360 to open a drawing placed on the Autodesk cloud.
You can find at the bottom of the screen: More info and CREATE (to start a new drawing).

Toolbars are always available but the workspace: AutoCAD Classic is missing so:
Either use the migration utility to retrieve its workspace.
Either display the toolbars.
You can migrate settings from a previous version.

To display drop-down menus:
Either on the keyboard: MENUBAR and answer 1 or from the list

Show toolbars: From the Tools -> Toolbars drop-down menu.
The status bar, access to Ortho Grille … changes look!
No longer displaying as text, the icons are bigger and more visible.
Click on the customization icon to display or not a particular tool.
Direct access to blocks in AutoCAD 2015:
Improved ribbon for insertion command.
A click on the insert icon displays a preview of the blocks in the current drawing.

Help is improved: by clicking on the icon – displays an arrow to find the function in the ribbon:

Object selection in AutoCAD 2015:
The highlighted display has slightly changed to more visible. (Place the mouse over the object).
Better visibility of the selection: highlighted display of a selection of objects: before and after selection.

Select by non-rectangular area by holding down the left button.

Better visibility when creating rows with a cache type or Isolation type.

Improved visibility and understanding when ordering Adjust and Extend: Preview the part of the object that will be adjusted or extended.
The overview for the commands is generalized, we have the overview during the commands: fitting, chamfer, offset, adjust, network copy, network ….
An icon appears next to the mouse during editing commands, a small icon is displayed, indicating the selection and the current command.
To order Distance el symbol? Is displayed:
Icon: icon change for command: quick selection, pan control (hand) selection of group or object pickadd
Example icon on the Move command
Object snap in AutoCAD 2015: Multiple snaps can now be selected from the list.

For the use of this version 2015 one gets used to this interface which displays better visibility in different areas:

Interface in AutoCAD 2015:
The ribbon is displayed with a dark theme (ribbon on a black background) by default.

Improvements on the Polyline in AutoCAD 2015:
It is possible to make a connection between a line segment and an arc of the polyline.
While drawing the polyline, create an arc you can now press the CTRL key to reverse the direction of the arc.
If you have divided the screen into several windows: you can resize windows easily with the mouse.
To split a window move the blue boundary and hold down the CTRL key.

Layer: View and sort layers in AutoCAD 2015:
With the version 2014 of AutoCAD the sorting had been corrected to obtain the following order: 1 then 2 then 3 and not 10 then 10 then 100 of the layers.
With the variable SORTORDER you can find the sorting of the layers as did the previous versions.

Easily Enable Hardware Acceleration:
Graphical Performance dialog box to activate the option: display of smoothed lines has been added.
Displays the + smooth lines. : Deletes the “stair” type of the lines.
And (depending on the video card)

Multi-line text and text editor in AutoCAD 2015:
The text editor is transparent, and therefore displays the drawing below the editor.
Change the length and height of the text, easily from the bottom right corner of the editor.

Automatic numbering in AutoCAD 2015: If the text begins with a number followed by a period or a parenthesis, AutoCAD applies automatic numbering.

AutoCAD 2016
AutoCAD 2014