I can produce a similar plot for your JMP 15 version, and in JMP 18
I assume you are getting by default the chart with the square markers and the large marker size, and the thick, red box plot outline. This would be because of the Preference settings for your copy of JMP 15. You will need to go to File=>Preferences=>Graphs and compare the same settings in JMP 18 Graph preferences, and to change them.
You can also manually make the changes just to the graph by right clicking on the legend marker and selecting Marker Color and Marker Size, and then right click on the graph and select Customize and there, change the box plot line color and line thickness
Jim