MacBook Pro (Retina, 13-inch, Early 2015) Thunderbolt 2 port for small second display (ASUS MB169C+ Portable USB Monitor for eg) MacBook Pro (Retina, 13-inch, Early 2015) Thunderbolt 2 port for small second display (ASUS MB169C+ Portable USB Monitor for eg) 

can I get a bidirectional adapter like the Thunderbolt 3 (USB-C) to Thunderbolt 2 Adapter? I believe the thunderbolt port puts out 9.9 W max and this display Power Consumption(Typical):&lt;7.5W* *measuring a screen brightness of 200 nits without audio/ USB/ Card reader connection)

basically I need a second portable screen 13" - 15" preferably type C like a large variety of modern displays available as mentioned above, preferably powered from the adapted thunderbolt 2 port etc, that way when I update the Macbook Pro later the screen will be usable on any updated model with Thunderbolt 3...

It doesn't have to be the above mentioned Asus screen but it looks the goods and no less then 1920x1080. I am not against the idea of utilizing the two thunderbolt ports one for display and one to power said display if required OR even use the HDMI port etc...  just as long as it works and powered by the Macbooks ports as the Macbook can be running from the wall charger as required...  

Again a portable setup preferably single cable.    recommendations and ideas much appreciated.
No.  This will not work.  You will need to get a display with its own power supply.

Thunderbolt 1/2 doesn’t support power delivery.  Even though Thunderbolt 3 does, connecting an adapter doesn’t magically make power appear.

The (up-to) 9W of power is bus power - you can’t  assume that because it’s there, it can be utilized, especially to power a device.  Remember, Thunderbolt can support up to 6 devices, so it wouldn’t make sense that a single device allocate most or all of the bus power.